diff --git a/integration/groups/groups-test.ts b/integration/groups/groups-test.ts
index 1bde75967..56af8a86e 100644
--- a/integration/groups/groups-test.ts
+++ b/integration/groups/groups-test.ts
@@ -41,9 +41,7 @@ describe('groups-test', () => {
     const result = GroupsOptionalTest.decode(data);
 
     expect(result).toEqual({
-      int1: 0,
       group: {
-        key: '',
         value: 'key',
         _unknownFields: {
           [(15 << 3) | 2]: [Buffer.from([2, 1, 2])]
@@ -79,14 +77,12 @@ describe('groups-test', () => {
       int1: [1, 2, 3, 4],
       group: [
         {
-          key: [],
           value: ['key'],
           _unknownFields: {
             [(10 << 3) | 2]: [Buffer.from([2, 0xa, 0xb])]
           }
         },
       ],
-      int3: [],
       _unknownFields: {
         [(27 << 3) | 2]: [Buffer.from([2, 0x10, 0x20])]
       }
@@ -133,7 +129,6 @@ describe('groups-test', () => {
     const result = GroupsNestedTest.decode(data);
 
     expect(result).toEqual({
-      int1: [],
       ...test
     });
   });
diff --git a/integration/groups/parameters.txt b/integration/groups/parameters.txt
index ae90c093e..07eb2b798 100644
--- a/integration/groups/parameters.txt
+++ b/integration/groups/parameters.txt
@@ -1 +1 @@
-useOptionals=all,unknownFields=true
\ No newline at end of file
+useOptionals=all,unknownFields=true,initializeFieldsAsUndefined=false
\ No newline at end of file
diff --git a/integration/groups/test.ts b/integration/groups/test.ts
index e73287df8..d420ba57e 100644
--- a/integration/groups/test.ts
+++ b/integration/groups/test.ts
@@ -7,44 +7,52 @@ export interface GroupsOptionalTest {
   int1?: number;
   group?: GroupsOptionalTest_Group;
   int3?: number;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GroupsOptionalTest_Group {
   key?: string;
   value?: string;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GroupsRepeatedTest {
   int1?: number[];
   group?: GroupsRepeatedTest_Group[];
   int3?: number[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GroupsRepeatedTest_Group {
   key?: string[];
   value?: string[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GroupsNestedTest {
   int1?: number[];
   group?: GroupsNestedTest_Group[];
   int3?: number[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GroupsNestedTest_Group {
   nested?: GroupsNestedTest_Group_Nested[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GroupsNestedTest_Group_Nested {
   nested2?: GroupsNestedTest_Group_Nested_Nested2[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GroupsNestedTest_Group_Nested_Nested2 {
   string1?: string;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 function createBaseGroupsOptionalTest(): GroupsOptionalTest {
-  return { int1: 0, group: undefined, int3: 0 };
+  return {};
 }
 
 export const GroupsOptionalTest = {
@@ -58,12 +66,12 @@ export const GroupsOptionalTest = {
     if (message.int3 !== undefined && message.int3 !== 0) {
       writer.uint32(24).int32(message.int3);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -79,7 +87,6 @@ export const GroupsOptionalTest = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsOptionalTest();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -111,10 +118,15 @@ export const GroupsOptionalTest = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -155,7 +167,7 @@ export const GroupsOptionalTest = {
 };
 
 function createBaseGroupsOptionalTest_Group(): GroupsOptionalTest_Group {
-  return { key: "", value: "" };
+  return {};
 }
 
 export const GroupsOptionalTest_Group = {
@@ -166,12 +178,12 @@ export const GroupsOptionalTest_Group = {
     if (message.value !== undefined && message.value !== "") {
       writer.uint32(18).string(message.value);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -187,7 +199,6 @@ export const GroupsOptionalTest_Group = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsOptionalTest_Group();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -212,10 +223,15 @@ export const GroupsOptionalTest_Group = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -247,7 +263,7 @@ export const GroupsOptionalTest_Group = {
 };
 
 function createBaseGroupsRepeatedTest(): GroupsRepeatedTest {
-  return { int1: [], group: [], int3: [] };
+  return {};
 }
 
 export const GroupsRepeatedTest = {
@@ -271,12 +287,12 @@ export const GroupsRepeatedTest = {
       }
       writer.ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -292,17 +308,22 @@ export const GroupsRepeatedTest = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsRepeatedTest();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
         case 1:
           if (tag == 8) {
+            if (message.int1 === undefined) {
+              message.int1 = [];
+            }
             message.int1!.push(reader.int32());
             continue;
           }
 
           if (tag == 10) {
+            if (message.int1 === undefined) {
+              message.int1 = [];
+            }
             const end2 = reader.uint32() + reader.pos;
             while (reader.pos < end2) {
               message.int1!.push(reader.int32());
@@ -317,15 +338,24 @@ export const GroupsRepeatedTest = {
             break;
           }
 
+          if (message.group === undefined) {
+            message.group = [];
+          }
           message.group!.push(GroupsRepeatedTest_Group.decode(reader));
           continue;
         case 3:
           if (tag == 24) {
+            if (message.int3 === undefined) {
+              message.int3 = [];
+            }
             message.int3!.push(reader.int32());
             continue;
           }
 
           if (tag == 26) {
+            if (message.int3 === undefined) {
+              message.int3 = [];
+            }
             const end2 = reader.uint32() + reader.pos;
             while (reader.pos < end2) {
               message.int3!.push(reader.int32());
@@ -342,10 +372,15 @@ export const GroupsRepeatedTest = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -395,7 +430,7 @@ export const GroupsRepeatedTest = {
 };
 
 function createBaseGroupsRepeatedTest_Group(): GroupsRepeatedTest_Group {
-  return { key: [], value: [] };
+  return {};
 }
 
 export const GroupsRepeatedTest_Group = {
@@ -410,12 +445,12 @@ export const GroupsRepeatedTest_Group = {
         writer.uint32(18).string(v!);
       }
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -431,7 +466,6 @@ export const GroupsRepeatedTest_Group = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsRepeatedTest_Group();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -440,6 +474,9 @@ export const GroupsRepeatedTest_Group = {
             break;
           }
 
+          if (message.key === undefined) {
+            message.key = [];
+          }
           message.key!.push(reader.string());
           continue;
         case 2:
@@ -447,6 +484,9 @@ export const GroupsRepeatedTest_Group = {
             break;
           }
 
+          if (message.value === undefined) {
+            message.value = [];
+          }
           message.value!.push(reader.string());
           continue;
       }
@@ -456,10 +496,15 @@ export const GroupsRepeatedTest_Group = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -502,7 +547,7 @@ export const GroupsRepeatedTest_Group = {
 };
 
 function createBaseGroupsNestedTest(): GroupsNestedTest {
-  return { int1: [], group: [], int3: [] };
+  return {};
 }
 
 export const GroupsNestedTest = {
@@ -526,12 +571,12 @@ export const GroupsNestedTest = {
       }
       writer.ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -547,17 +592,22 @@ export const GroupsNestedTest = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsNestedTest();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
         case 1:
           if (tag == 8) {
+            if (message.int1 === undefined) {
+              message.int1 = [];
+            }
             message.int1!.push(reader.int32());
             continue;
           }
 
           if (tag == 10) {
+            if (message.int1 === undefined) {
+              message.int1 = [];
+            }
             const end2 = reader.uint32() + reader.pos;
             while (reader.pos < end2) {
               message.int1!.push(reader.int32());
@@ -572,15 +622,24 @@ export const GroupsNestedTest = {
             break;
           }
 
+          if (message.group === undefined) {
+            message.group = [];
+          }
           message.group!.push(GroupsNestedTest_Group.decode(reader));
           continue;
         case 3:
           if (tag == 24) {
+            if (message.int3 === undefined) {
+              message.int3 = [];
+            }
             message.int3!.push(reader.int32());
             continue;
           }
 
           if (tag == 26) {
+            if (message.int3 === undefined) {
+              message.int3 = [];
+            }
             const end2 = reader.uint32() + reader.pos;
             while (reader.pos < end2) {
               message.int3!.push(reader.int32());
@@ -597,10 +656,15 @@ export const GroupsNestedTest = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -650,7 +714,7 @@ export const GroupsNestedTest = {
 };
 
 function createBaseGroupsNestedTest_Group(): GroupsNestedTest_Group {
-  return { nested: [] };
+  return {};
 }
 
 export const GroupsNestedTest_Group = {
@@ -660,12 +724,12 @@ export const GroupsNestedTest_Group = {
         GroupsNestedTest_Group_Nested.encode(v!, writer.uint32(11)).uint32(12);
       }
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -681,7 +745,6 @@ export const GroupsNestedTest_Group = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsNestedTest_Group();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -690,6 +753,9 @@ export const GroupsNestedTest_Group = {
             break;
           }
 
+          if (message.nested === undefined) {
+            message.nested = [];
+          }
           message.nested!.push(GroupsNestedTest_Group_Nested.decode(reader));
           continue;
       }
@@ -699,10 +765,15 @@ export const GroupsNestedTest_Group = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -740,7 +811,7 @@ export const GroupsNestedTest_Group = {
 };
 
 function createBaseGroupsNestedTest_Group_Nested(): GroupsNestedTest_Group_Nested {
-  return { nested2: [] };
+  return {};
 }
 
 export const GroupsNestedTest_Group_Nested = {
@@ -750,12 +821,12 @@ export const GroupsNestedTest_Group_Nested = {
         GroupsNestedTest_Group_Nested_Nested2.encode(v!, writer.uint32(19)).uint32(20);
       }
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -771,7 +842,6 @@ export const GroupsNestedTest_Group_Nested = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsNestedTest_Group_Nested();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -780,6 +850,9 @@ export const GroupsNestedTest_Group_Nested = {
             break;
           }
 
+          if (message.nested2 === undefined) {
+            message.nested2 = [];
+          }
           message.nested2!.push(GroupsNestedTest_Group_Nested_Nested2.decode(reader));
           continue;
       }
@@ -789,10 +862,15 @@ export const GroupsNestedTest_Group_Nested = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -832,7 +910,7 @@ export const GroupsNestedTest_Group_Nested = {
 };
 
 function createBaseGroupsNestedTest_Group_Nested_Nested2(): GroupsNestedTest_Group_Nested_Nested2 {
-  return { string1: "" };
+  return {};
 }
 
 export const GroupsNestedTest_Group_Nested_Nested2 = {
@@ -840,12 +918,12 @@ export const GroupsNestedTest_Group_Nested_Nested2 = {
     if (message.string1 !== undefined && message.string1 !== "") {
       writer.uint32(10).string(message.string1);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -861,7 +939,6 @@ export const GroupsNestedTest_Group_Nested_Nested2 = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGroupsNestedTest_Group_Nested_Nested2();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -879,10 +956,15 @@ export const GroupsNestedTest_Group_Nested_Nested2 = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      if (message._unknownFields === undefined) {
+        message._unknownFields = {};
+      }
+
+      const list = message._unknownFields[tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields[tag] = [buf];
       } else {
         list.push(buf);
       }
diff --git a/integration/unknown-fields/google/protobuf/compiler/plugin.ts b/integration/unknown-fields/google/protobuf/compiler/plugin.ts
index 2a81f4c83..d3efd57b3 100644
--- a/integration/unknown-fields/google/protobuf/compiler/plugin.ts
+++ b/integration/unknown-fields/google/protobuf/compiler/plugin.ts
@@ -15,6 +15,7 @@ export interface Version {
    * be empty for mainline stable releases.
    */
   suffix: string;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** An encoded CodeGeneratorRequest is written to the plugin's stdin. */
@@ -46,6 +47,7 @@ export interface CodeGeneratorRequest {
   protoFile: FileDescriptorProto[];
   /** The version number of protocol compiler. */
   compilerVersion: Version | undefined;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** The plugin writes an encoded CodeGeneratorResponse to stdout. */
@@ -67,6 +69,7 @@ export interface CodeGeneratorResponse {
    */
   supportedFeatures: number;
   file: CodeGeneratorResponse_File[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Sync with code_generator.h. */
@@ -140,10 +143,11 @@ export interface CodeGeneratorResponse_File {
    * into the code generation metadata for the generated files.
    */
   generatedCodeInfo: GeneratedCodeInfo | undefined;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 function createBaseVersion(): Version {
-  return { major: 0, minor: 0, patch: 0, suffix: "" };
+  return { major: 0, minor: 0, patch: 0, suffix: "", _unknownFields: {} };
 }
 
 export const Version = {
@@ -160,12 +164,12 @@ export const Version = {
     if (message.suffix !== "") {
       writer.uint32(34).string(message.suffix);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -181,7 +185,6 @@ export const Version = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseVersion();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -220,10 +223,11 @@ export const Version = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -233,7 +237,7 @@ export const Version = {
 };
 
 function createBaseCodeGeneratorRequest(): CodeGeneratorRequest {
-  return { fileToGenerate: [], parameter: "", protoFile: [], compilerVersion: undefined };
+  return { fileToGenerate: [], parameter: "", protoFile: [], compilerVersion: undefined, _unknownFields: {} };
 }
 
 export const CodeGeneratorRequest = {
@@ -250,12 +254,12 @@ export const CodeGeneratorRequest = {
     if (message.compilerVersion !== undefined) {
       Version.encode(message.compilerVersion, writer.uint32(26).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -271,7 +275,6 @@ export const CodeGeneratorRequest = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseCodeGeneratorRequest();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -310,10 +313,11 @@ export const CodeGeneratorRequest = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -323,7 +327,7 @@ export const CodeGeneratorRequest = {
 };
 
 function createBaseCodeGeneratorResponse(): CodeGeneratorResponse {
-  return { error: "", supportedFeatures: 0, file: [] };
+  return { error: "", supportedFeatures: 0, file: [], _unknownFields: {} };
 }
 
 export const CodeGeneratorResponse = {
@@ -337,12 +341,12 @@ export const CodeGeneratorResponse = {
     for (const v of message.file) {
       CodeGeneratorResponse_File.encode(v!, writer.uint32(122).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -358,7 +362,6 @@ export const CodeGeneratorResponse = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseCodeGeneratorResponse();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -390,10 +393,11 @@ export const CodeGeneratorResponse = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -403,7 +407,7 @@ export const CodeGeneratorResponse = {
 };
 
 function createBaseCodeGeneratorResponse_File(): CodeGeneratorResponse_File {
-  return { name: "", insertionPoint: "", content: "", generatedCodeInfo: undefined };
+  return { name: "", insertionPoint: "", content: "", generatedCodeInfo: undefined, _unknownFields: {} };
 }
 
 export const CodeGeneratorResponse_File = {
@@ -420,12 +424,12 @@ export const CodeGeneratorResponse_File = {
     if (message.generatedCodeInfo !== undefined) {
       GeneratedCodeInfo.encode(message.generatedCodeInfo, writer.uint32(130).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -441,7 +445,6 @@ export const CodeGeneratorResponse_File = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseCodeGeneratorResponse_File();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -480,10 +483,11 @@ export const CodeGeneratorResponse_File = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
diff --git a/integration/unknown-fields/google/protobuf/descriptor.ts b/integration/unknown-fields/google/protobuf/descriptor.ts
index 5f136849c..8013750f9 100644
--- a/integration/unknown-fields/google/protobuf/descriptor.ts
+++ b/integration/unknown-fields/google/protobuf/descriptor.ts
@@ -10,6 +10,7 @@ export const protobufPackage = "google.protobuf";
  */
 export interface FileDescriptorSet {
   file: FileDescriptorProto[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Describes a complete .proto file. */
@@ -49,6 +50,7 @@ export interface FileDescriptorProto {
    * The supported values are "proto2" and "proto3".
    */
   syntax: string;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Describes a message type. */
@@ -67,6 +69,7 @@ export interface DescriptorProto {
    * A given name may only be reserved once.
    */
   reservedName: string[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface DescriptorProto_ExtensionRange {
@@ -75,6 +78,7 @@ export interface DescriptorProto_ExtensionRange {
   /** Exclusive. */
   end: number;
   options: ExtensionRangeOptions | undefined;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /**
@@ -87,11 +91,13 @@ export interface DescriptorProto_ReservedRange {
   start: number;
   /** Exclusive. */
   end: number;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface ExtensionRangeOptions {
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Describes a field within a message. */
@@ -164,6 +170,7 @@ export interface FieldDescriptorProto {
    * optional with `LABEL_OPTIONAL`.
    */
   proto3Optional: boolean;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export enum FieldDescriptorProto_Type {
@@ -222,6 +229,7 @@ export enum FieldDescriptorProto_Label {
 export interface OneofDescriptorProto {
   name: string;
   options: OneofOptions | undefined;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Describes an enum type. */
@@ -242,6 +250,7 @@ export interface EnumDescriptorProto {
    * be reserved once.
    */
   reservedName: string[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /**
@@ -257,6 +266,7 @@ export interface EnumDescriptorProto_EnumReservedRange {
   start: number;
   /** Inclusive. */
   end: number;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Describes a value within an enum. */
@@ -264,6 +274,7 @@ export interface EnumValueDescriptorProto {
   name: string;
   number: number;
   options: EnumValueOptions | undefined;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Describes a service. */
@@ -271,6 +282,7 @@ export interface ServiceDescriptorProto {
   name: string;
   method: MethodDescriptorProto[];
   options: ServiceOptions | undefined;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Describes a method of a service. */
@@ -289,6 +301,7 @@ export interface MethodDescriptorProto {
   clientStreaming: boolean;
   /** Identifies if server streams multiple server messages */
   serverStreaming: boolean;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface FileOptions {
@@ -410,6 +423,7 @@ export interface FileOptions {
    * See the documentation for the "Options" section above.
    */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /** Generated classes can be optimized for speed or code size. */
@@ -484,6 +498,7 @@ export interface MessageOptions {
   mapEntry: boolean;
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface FieldOptions {
@@ -557,6 +572,7 @@ export interface FieldOptions {
   weak: boolean;
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export enum FieldOptions_CType {
@@ -580,6 +596,7 @@ export enum FieldOptions_JSType {
 export interface OneofOptions {
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface EnumOptions {
@@ -597,6 +614,7 @@ export interface EnumOptions {
   deprecated: boolean;
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface EnumValueOptions {
@@ -609,6 +627,7 @@ export interface EnumValueOptions {
   deprecated: boolean;
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface ServiceOptions {
@@ -621,6 +640,7 @@ export interface ServiceOptions {
   deprecated: boolean;
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface MethodOptions {
@@ -634,6 +654,7 @@ export interface MethodOptions {
   idempotencyLevel: MethodOptions_IdempotencyLevel;
   /** The parser stores options it doesn't recognize here. See above. */
   uninterpretedOption: UninterpretedOption[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /**
@@ -670,6 +691,7 @@ export interface UninterpretedOption {
   doubleValue: number;
   stringValue: Uint8Array;
   aggregateValue: string;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /**
@@ -682,6 +704,7 @@ export interface UninterpretedOption {
 export interface UninterpretedOption_NamePart {
   namePart: string;
   isExtension: boolean;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /**
@@ -735,6 +758,7 @@ export interface SourceCodeInfo {
    *   be recorded in the future.
    */
   location: SourceCodeInfo_Location[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface SourceCodeInfo_Location {
@@ -824,6 +848,7 @@ export interface SourceCodeInfo_Location {
   leadingComments: string;
   trailingComments: string;
   leadingDetachedComments: string[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 /**
@@ -837,6 +862,7 @@ export interface GeneratedCodeInfo {
    * of its generating .proto file.
    */
   annotation: GeneratedCodeInfo_Annotation[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface GeneratedCodeInfo_Annotation {
@@ -858,10 +884,11 @@ export interface GeneratedCodeInfo_Annotation {
    * the last relevant byte (so the length of the text = end - begin).
    */
   end: number;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 function createBaseFileDescriptorSet(): FileDescriptorSet {
-  return { file: [] };
+  return { file: [], _unknownFields: {} };
 }
 
 export const FileDescriptorSet = {
@@ -869,12 +896,12 @@ export const FileDescriptorSet = {
     for (const v of message.file) {
       FileDescriptorProto.encode(v!, writer.uint32(10).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -890,7 +917,6 @@ export const FileDescriptorSet = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseFileDescriptorSet();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -908,10 +934,11 @@ export const FileDescriptorSet = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -934,6 +961,7 @@ function createBaseFileDescriptorProto(): FileDescriptorProto {
     options: undefined,
     sourceCodeInfo: undefined,
     syntax: "",
+    _unknownFields: {},
   };
 }
 
@@ -979,12 +1007,12 @@ export const FileDescriptorProto = {
     if (message.syntax !== "") {
       writer.uint32(98).string(message.syntax);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1000,7 +1028,6 @@ export const FileDescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseFileDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1113,10 +1140,11 @@ export const FileDescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1137,6 +1165,7 @@ function createBaseDescriptorProto(): DescriptorProto {
     options: undefined,
     reservedRange: [],
     reservedName: [],
+    _unknownFields: {},
   };
 }
 
@@ -1172,12 +1201,12 @@ export const DescriptorProto = {
     for (const v of message.reservedName) {
       writer.uint32(82).string(v!);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1193,7 +1222,6 @@ export const DescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1274,10 +1302,11 @@ export const DescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1287,7 +1316,7 @@ export const DescriptorProto = {
 };
 
 function createBaseDescriptorProto_ExtensionRange(): DescriptorProto_ExtensionRange {
-  return { start: 0, end: 0, options: undefined };
+  return { start: 0, end: 0, options: undefined, _unknownFields: {} };
 }
 
 export const DescriptorProto_ExtensionRange = {
@@ -1301,12 +1330,12 @@ export const DescriptorProto_ExtensionRange = {
     if (message.options !== undefined) {
       ExtensionRangeOptions.encode(message.options, writer.uint32(26).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1322,7 +1351,6 @@ export const DescriptorProto_ExtensionRange = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseDescriptorProto_ExtensionRange();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1354,10 +1382,11 @@ export const DescriptorProto_ExtensionRange = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1367,7 +1396,7 @@ export const DescriptorProto_ExtensionRange = {
 };
 
 function createBaseDescriptorProto_ReservedRange(): DescriptorProto_ReservedRange {
-  return { start: 0, end: 0 };
+  return { start: 0, end: 0, _unknownFields: {} };
 }
 
 export const DescriptorProto_ReservedRange = {
@@ -1378,12 +1407,12 @@ export const DescriptorProto_ReservedRange = {
     if (message.end !== 0) {
       writer.uint32(16).int32(message.end);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1399,7 +1428,6 @@ export const DescriptorProto_ReservedRange = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseDescriptorProto_ReservedRange();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1424,10 +1452,11 @@ export const DescriptorProto_ReservedRange = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1437,7 +1466,7 @@ export const DescriptorProto_ReservedRange = {
 };
 
 function createBaseExtensionRangeOptions(): ExtensionRangeOptions {
-  return { uninterpretedOption: [] };
+  return { uninterpretedOption: [], _unknownFields: {} };
 }
 
 export const ExtensionRangeOptions = {
@@ -1445,12 +1474,12 @@ export const ExtensionRangeOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1466,7 +1495,6 @@ export const ExtensionRangeOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseExtensionRangeOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1484,10 +1512,11 @@ export const ExtensionRangeOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1509,6 +1538,7 @@ function createBaseFieldDescriptorProto(): FieldDescriptorProto {
     jsonName: "",
     options: undefined,
     proto3Optional: false,
+    _unknownFields: {},
   };
 }
 
@@ -1547,12 +1577,12 @@ export const FieldDescriptorProto = {
     if (message.proto3Optional === true) {
       writer.uint32(136).bool(message.proto3Optional);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1568,7 +1598,6 @@ export const FieldDescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseFieldDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1656,10 +1685,11 @@ export const FieldDescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1669,7 +1699,7 @@ export const FieldDescriptorProto = {
 };
 
 function createBaseOneofDescriptorProto(): OneofDescriptorProto {
-  return { name: "", options: undefined };
+  return { name: "", options: undefined, _unknownFields: {} };
 }
 
 export const OneofDescriptorProto = {
@@ -1680,12 +1710,12 @@ export const OneofDescriptorProto = {
     if (message.options !== undefined) {
       OneofOptions.encode(message.options, writer.uint32(18).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1701,7 +1731,6 @@ export const OneofDescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseOneofDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1726,10 +1755,11 @@ export const OneofDescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1739,7 +1769,7 @@ export const OneofDescriptorProto = {
 };
 
 function createBaseEnumDescriptorProto(): EnumDescriptorProto {
-  return { name: "", value: [], options: undefined, reservedRange: [], reservedName: [] };
+  return { name: "", value: [], options: undefined, reservedRange: [], reservedName: [], _unknownFields: {} };
 }
 
 export const EnumDescriptorProto = {
@@ -1759,12 +1789,12 @@ export const EnumDescriptorProto = {
     for (const v of message.reservedName) {
       writer.uint32(42).string(v!);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1780,7 +1810,6 @@ export const EnumDescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseEnumDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1826,10 +1855,11 @@ export const EnumDescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1839,7 +1869,7 @@ export const EnumDescriptorProto = {
 };
 
 function createBaseEnumDescriptorProto_EnumReservedRange(): EnumDescriptorProto_EnumReservedRange {
-  return { start: 0, end: 0 };
+  return { start: 0, end: 0, _unknownFields: {} };
 }
 
 export const EnumDescriptorProto_EnumReservedRange = {
@@ -1850,12 +1880,12 @@ export const EnumDescriptorProto_EnumReservedRange = {
     if (message.end !== 0) {
       writer.uint32(16).int32(message.end);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1871,7 +1901,6 @@ export const EnumDescriptorProto_EnumReservedRange = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseEnumDescriptorProto_EnumReservedRange();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1896,10 +1925,11 @@ export const EnumDescriptorProto_EnumReservedRange = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1909,7 +1939,7 @@ export const EnumDescriptorProto_EnumReservedRange = {
 };
 
 function createBaseEnumValueDescriptorProto(): EnumValueDescriptorProto {
-  return { name: "", number: 0, options: undefined };
+  return { name: "", number: 0, options: undefined, _unknownFields: {} };
 }
 
 export const EnumValueDescriptorProto = {
@@ -1923,12 +1953,12 @@ export const EnumValueDescriptorProto = {
     if (message.options !== undefined) {
       EnumValueOptions.encode(message.options, writer.uint32(26).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -1944,7 +1974,6 @@ export const EnumValueDescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseEnumValueDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -1976,10 +2005,11 @@ export const EnumValueDescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -1989,7 +2019,7 @@ export const EnumValueDescriptorProto = {
 };
 
 function createBaseServiceDescriptorProto(): ServiceDescriptorProto {
-  return { name: "", method: [], options: undefined };
+  return { name: "", method: [], options: undefined, _unknownFields: {} };
 }
 
 export const ServiceDescriptorProto = {
@@ -2003,12 +2033,12 @@ export const ServiceDescriptorProto = {
     if (message.options !== undefined) {
       ServiceOptions.encode(message.options, writer.uint32(26).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2024,7 +2054,6 @@ export const ServiceDescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseServiceDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2056,10 +2085,11 @@ export const ServiceDescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2076,6 +2106,7 @@ function createBaseMethodDescriptorProto(): MethodDescriptorProto {
     options: undefined,
     clientStreaming: false,
     serverStreaming: false,
+    _unknownFields: {},
   };
 }
 
@@ -2099,12 +2130,12 @@ export const MethodDescriptorProto = {
     if (message.serverStreaming === true) {
       writer.uint32(48).bool(message.serverStreaming);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2120,7 +2151,6 @@ export const MethodDescriptorProto = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseMethodDescriptorProto();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2173,10 +2203,11 @@ export const MethodDescriptorProto = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2208,6 +2239,7 @@ function createBaseFileOptions(): FileOptions {
     phpMetadataNamespace: "",
     rubyPackage: "",
     uninterpretedOption: [],
+    _unknownFields: {},
   };
 }
 
@@ -2276,12 +2308,12 @@ export const FileOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2297,7 +2329,6 @@ export const FileOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseFileOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2455,10 +2486,11 @@ export const FileOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2474,6 +2506,7 @@ function createBaseMessageOptions(): MessageOptions {
     deprecated: false,
     mapEntry: false,
     uninterpretedOption: [],
+    _unknownFields: {},
   };
 }
 
@@ -2494,12 +2527,12 @@ export const MessageOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2515,7 +2548,6 @@ export const MessageOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseMessageOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2561,10 +2593,11 @@ export const MessageOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2574,7 +2607,16 @@ export const MessageOptions = {
 };
 
 function createBaseFieldOptions(): FieldOptions {
-  return { ctype: 0, packed: false, jstype: 0, lazy: false, deprecated: false, weak: false, uninterpretedOption: [] };
+  return {
+    ctype: 0,
+    packed: false,
+    jstype: 0,
+    lazy: false,
+    deprecated: false,
+    weak: false,
+    uninterpretedOption: [],
+    _unknownFields: {},
+  };
 }
 
 export const FieldOptions = {
@@ -2600,12 +2642,12 @@ export const FieldOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2621,7 +2663,6 @@ export const FieldOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseFieldOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2681,10 +2722,11 @@ export const FieldOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2694,7 +2736,7 @@ export const FieldOptions = {
 };
 
 function createBaseOneofOptions(): OneofOptions {
-  return { uninterpretedOption: [] };
+  return { uninterpretedOption: [], _unknownFields: {} };
 }
 
 export const OneofOptions = {
@@ -2702,12 +2744,12 @@ export const OneofOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2723,7 +2765,6 @@ export const OneofOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseOneofOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2741,10 +2782,11 @@ export const OneofOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2754,7 +2796,7 @@ export const OneofOptions = {
 };
 
 function createBaseEnumOptions(): EnumOptions {
-  return { allowAlias: false, deprecated: false, uninterpretedOption: [] };
+  return { allowAlias: false, deprecated: false, uninterpretedOption: [], _unknownFields: {} };
 }
 
 export const EnumOptions = {
@@ -2768,12 +2810,12 @@ export const EnumOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2789,7 +2831,6 @@ export const EnumOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseEnumOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2821,10 +2862,11 @@ export const EnumOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2834,7 +2876,7 @@ export const EnumOptions = {
 };
 
 function createBaseEnumValueOptions(): EnumValueOptions {
-  return { deprecated: false, uninterpretedOption: [] };
+  return { deprecated: false, uninterpretedOption: [], _unknownFields: {} };
 }
 
 export const EnumValueOptions = {
@@ -2845,12 +2887,12 @@ export const EnumValueOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2866,7 +2908,6 @@ export const EnumValueOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseEnumValueOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2891,10 +2932,11 @@ export const EnumValueOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2904,7 +2946,7 @@ export const EnumValueOptions = {
 };
 
 function createBaseServiceOptions(): ServiceOptions {
-  return { deprecated: false, uninterpretedOption: [] };
+  return { deprecated: false, uninterpretedOption: [], _unknownFields: {} };
 }
 
 export const ServiceOptions = {
@@ -2915,12 +2957,12 @@ export const ServiceOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -2936,7 +2978,6 @@ export const ServiceOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseServiceOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -2961,10 +3002,11 @@ export const ServiceOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -2974,7 +3016,7 @@ export const ServiceOptions = {
 };
 
 function createBaseMethodOptions(): MethodOptions {
-  return { deprecated: false, idempotencyLevel: 0, uninterpretedOption: [] };
+  return { deprecated: false, idempotencyLevel: 0, uninterpretedOption: [], _unknownFields: {} };
 }
 
 export const MethodOptions = {
@@ -2988,12 +3030,12 @@ export const MethodOptions = {
     for (const v of message.uninterpretedOption) {
       UninterpretedOption.encode(v!, writer.uint32(7994).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -3009,7 +3051,6 @@ export const MethodOptions = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseMethodOptions();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -3041,10 +3082,11 @@ export const MethodOptions = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -3062,6 +3104,7 @@ function createBaseUninterpretedOption(): UninterpretedOption {
     doubleValue: 0,
     stringValue: new Uint8Array(),
     aggregateValue: "",
+    _unknownFields: {},
   };
 }
 
@@ -3088,12 +3131,12 @@ export const UninterpretedOption = {
     if (message.aggregateValue !== "") {
       writer.uint32(66).string(message.aggregateValue);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -3109,7 +3152,6 @@ export const UninterpretedOption = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseUninterpretedOption();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -3169,10 +3211,11 @@ export const UninterpretedOption = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -3182,7 +3225,7 @@ export const UninterpretedOption = {
 };
 
 function createBaseUninterpretedOption_NamePart(): UninterpretedOption_NamePart {
-  return { namePart: "", isExtension: false };
+  return { namePart: "", isExtension: false, _unknownFields: {} };
 }
 
 export const UninterpretedOption_NamePart = {
@@ -3193,12 +3236,12 @@ export const UninterpretedOption_NamePart = {
     if (message.isExtension === true) {
       writer.uint32(16).bool(message.isExtension);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -3214,7 +3257,6 @@ export const UninterpretedOption_NamePart = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseUninterpretedOption_NamePart();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -3239,10 +3281,11 @@ export const UninterpretedOption_NamePart = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -3252,7 +3295,7 @@ export const UninterpretedOption_NamePart = {
 };
 
 function createBaseSourceCodeInfo(): SourceCodeInfo {
-  return { location: [] };
+  return { location: [], _unknownFields: {} };
 }
 
 export const SourceCodeInfo = {
@@ -3260,12 +3303,12 @@ export const SourceCodeInfo = {
     for (const v of message.location) {
       SourceCodeInfo_Location.encode(v!, writer.uint32(10).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -3281,7 +3324,6 @@ export const SourceCodeInfo = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseSourceCodeInfo();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -3299,10 +3341,11 @@ export const SourceCodeInfo = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -3312,7 +3355,14 @@ export const SourceCodeInfo = {
 };
 
 function createBaseSourceCodeInfo_Location(): SourceCodeInfo_Location {
-  return { path: [], span: [], leadingComments: "", trailingComments: "", leadingDetachedComments: [] };
+  return {
+    path: [],
+    span: [],
+    leadingComments: "",
+    trailingComments: "",
+    leadingDetachedComments: [],
+    _unknownFields: {},
+  };
 }
 
 export const SourceCodeInfo_Location = {
@@ -3336,12 +3386,12 @@ export const SourceCodeInfo_Location = {
     for (const v of message.leadingDetachedComments) {
       writer.uint32(50).string(v!);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -3357,7 +3407,6 @@ export const SourceCodeInfo_Location = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseSourceCodeInfo_Location();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -3421,10 +3470,11 @@ export const SourceCodeInfo_Location = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -3434,7 +3484,7 @@ export const SourceCodeInfo_Location = {
 };
 
 function createBaseGeneratedCodeInfo(): GeneratedCodeInfo {
-  return { annotation: [] };
+  return { annotation: [], _unknownFields: {} };
 }
 
 export const GeneratedCodeInfo = {
@@ -3442,12 +3492,12 @@ export const GeneratedCodeInfo = {
     for (const v of message.annotation) {
       GeneratedCodeInfo_Annotation.encode(v!, writer.uint32(10).fork()).ldelim();
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -3463,7 +3513,6 @@ export const GeneratedCodeInfo = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGeneratedCodeInfo();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -3481,10 +3530,11 @@ export const GeneratedCodeInfo = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -3494,7 +3544,7 @@ export const GeneratedCodeInfo = {
 };
 
 function createBaseGeneratedCodeInfo_Annotation(): GeneratedCodeInfo_Annotation {
-  return { path: [], sourceFile: "", begin: 0, end: 0 };
+  return { path: [], sourceFile: "", begin: 0, end: 0, _unknownFields: {} };
 }
 
 export const GeneratedCodeInfo_Annotation = {
@@ -3513,12 +3563,12 @@ export const GeneratedCodeInfo_Annotation = {
     if (message.end !== 0) {
       writer.uint32(32).int32(message.end);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -3534,7 +3584,6 @@ export const GeneratedCodeInfo_Annotation = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseGeneratedCodeInfo_Annotation();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -3582,10 +3631,11 @@ export const GeneratedCodeInfo_Annotation = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
diff --git a/integration/unknown-fields/options.ts b/integration/unknown-fields/options.ts
index 2bb562428..d0f677191 100644
--- a/integration/unknown-fields/options.ts
+++ b/integration/unknown-fields/options.ts
@@ -14,16 +14,19 @@ export interface MyMessage {
   foo2?: number | undefined;
   bar?: string | undefined;
   quux?: string | undefined;
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface RequestType {
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 export interface ResponseType {
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 function createBaseMyMessage(): MyMessage {
-  return { foo: undefined, foo2: undefined, bar: undefined, quux: undefined };
+  return { foo: undefined, foo2: undefined, bar: undefined, quux: undefined, _unknownFields: {} };
 }
 
 export const MyMessage = {
@@ -40,12 +43,12 @@ export const MyMessage = {
     if (message.quux !== undefined) {
       writer.uint32(34).string(message.quux);
     }
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -61,7 +64,6 @@ export const MyMessage = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseMyMessage();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -100,10 +102,11 @@ export const MyMessage = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -113,17 +116,17 @@ export const MyMessage = {
 };
 
 function createBaseRequestType(): RequestType {
-  return {};
+  return { _unknownFields: {} };
 }
 
 export const RequestType = {
   encode(message: RequestType, writer: _m0.Writer = _m0.Writer.create()): _m0.Writer {
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -139,7 +142,6 @@ export const RequestType = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseRequestType();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -150,10 +152,11 @@ export const RequestType = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
@@ -163,17 +166,17 @@ export const RequestType = {
 };
 
 function createBaseResponseType(): ResponseType {
-  return {};
+  return { _unknownFields: {} };
 }
 
 export const ResponseType = {
   encode(message: ResponseType, writer: _m0.Writer = _m0.Writer.create()): _m0.Writer {
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -189,7 +192,6 @@ export const ResponseType = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseResponseType();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -200,10 +202,11 @@ export const ResponseType = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
diff --git a/integration/unknown-fields/something/something.ts b/integration/unknown-fields/something/something.ts
index 21c5283c1..b9d2a9bf9 100644
--- a/integration/unknown-fields/something/something.ts
+++ b/integration/unknown-fields/something/something.ts
@@ -6,10 +6,11 @@ export const protobufPackage = "something";
 export interface Something {
   hello: string;
   foo: number[];
+  _unknownFields?: { [key: number]: Uint8Array[] };
 }
 
 function createBaseSomething(): Something {
-  return { hello: "", foo: [] };
+  return { hello: "", foo: [], _unknownFields: {} };
 }
 
 export const Something = {
@@ -22,12 +23,12 @@ export const Something = {
       writer.int32(v);
     }
     writer.ldelim();
-    if ("_unknownFields" in message) {
-      const msgUnknownFields: any = (message as any)["_unknownFields"];
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)["_push"](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
@@ -43,7 +44,6 @@ export const Something = {
     const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = createBaseSomething();
-    (message as any)._unknownFields = {};
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -77,10 +77,11 @@ export const Something = {
       const startPos = reader.pos;
       reader.skipType(tag & 7);
       const buf = reader.buf.slice(startPos, reader.pos);
-      const list = (message as any)._unknownFields[tag];
+
+      const list = message._unknownFields![tag];
 
       if (list === undefined) {
-        (message as any)._unknownFields[tag] = [buf];
+        message._unknownFields![tag] = [buf];
       } else {
         list.push(buf);
       }
diff --git a/src/generate-generic-service-definition.ts b/src/generate-generic-service-definition.ts
index 963fd9d9e..c9a0e1723 100644
--- a/src/generate-generic-service-definition.ts
+++ b/src/generate-generic-service-definition.ts
@@ -88,14 +88,13 @@ function generateMethodOptions(ctx: Context, options: MethodOptions | undefined)
       chunks.push(code`idempotencyLevel: 'NO_SIDE_EFFECTS',`);
     }
 
-    if ("_unknownFields" in options) {
-      const msgUnknownFields: any = (options as any)["_unknownFields"];
+    if (options._unknownFields !== undefined) {
       const unknownFieldsChunks: Code[] = [];
 
       unknownFieldsChunks.push(code`{`);
 
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+      for (const key in options._unknownFields) {
+        const values = options._unknownFields[key];
         const valuesChunks: Code[] = [];
 
         for (const value of values) {
diff --git a/src/main.ts b/src/main.ts
index 6d15c1f23..8d4b10086 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -821,6 +821,10 @@ function generateInterfaceDeclaration(
     chunks.push(code`${maybeReadonly(options)}${name}${q}: ${type}, `);
   });
 
+  if (ctx.options.unknownFields) {
+    chunks.push(code`_unknownFields?: {[key: number]: Uint8Array[]},`);
+  }
+
   chunks.push(code`}`);
   return joinCode(chunks, { on: "\n" });
 }
@@ -915,6 +919,10 @@ function generateBaseInstanceFactory(
     fields.unshift(code`$type: '${fullTypeName}'`);
   }
 
+  if (ctx.options.unknownFields && ctx.options.initializeFieldsAsUndefined) {
+    fields.push(code`_unknownFields: {}`);
+  }
+
   return code`
     function createBase${fullName}(): ${fullName} {
       return { ${joinCode(fields, { on: "," })} };
@@ -946,10 +954,6 @@ function generateDecode(ctx: Context, fullName: string, messageDesc: DescriptorP
 
   chunks.push(code`const message = ${createBase}${maybeAsAny(options)};`);
 
-  if (options.unknownFields) {
-    chunks.push(code`(message as any)._unknownFields = {}`);
-  }
-
   // start the tag loop
   chunks.push(code`
     while (reader.pos < end) {
@@ -1105,16 +1109,28 @@ function generateDecode(ctx: Context, fullName: string, messageDesc: DescriptorP
   `);
 
   if (options.unknownFields) {
+    let unknownFieldsInitializerSnippet = "";
+    let maybeNonNullAssertion = options.initializeFieldsAsUndefined ? "!" : "";
+
+    if (!options.initializeFieldsAsUndefined) {
+      unknownFieldsInitializerSnippet = `
+        if(message._unknownFields === undefined)
+          message._unknownFields = {};
+      `;
+    }
+
     chunks.push(code`
-        const startPos = reader.pos;
-        reader.skipType(tag & 7);
-        const buf = reader.buf.slice(startPos, reader.pos);
-        const list = (message as any)._unknownFields[tag];
+      const startPos = reader.pos;
+      reader.skipType(tag & 7);
+      const buf = reader.buf.slice(startPos, reader.pos);
+
+      ${unknownFieldsInitializerSnippet}
+      const list = message._unknownFields${maybeNonNullAssertion}[tag];
 
-        if(list === undefined)
-          (message as any)._unknownFields[tag] = [buf];
-        else
-          list.push(buf);
+      if(list === undefined)
+        message._unknownFields${maybeNonNullAssertion}[tag] = [buf];
+      else
+        list.push(buf);
     `);
   } else {
     chunks.push(code`
@@ -1336,12 +1352,12 @@ function generateEncode(ctx: Context, fullName: string, messageDesc: DescriptorP
   });
 
   if (options.unknownFields) {
-    chunks.push(code`if ('_unknownFields' in message) {
-      const msgUnknownFields: any = (message as any)['_unknownFields']
-      for (const key of Object.keys(msgUnknownFields)) {
-        const values = msgUnknownFields[key] as Uint8Array[];
+    chunks.push(code`if (message._unknownFields !== undefined) {
+      for (const key in message._unknownFields) {
+        const values = message._unknownFields[key];
+        const tag = parseInt(key, 10);
         for (const value of values) {
-          writer.uint32(parseInt(key, 10));
+          writer.uint32(tag);
           (writer as any)['_push'](
             (val: Uint8Array, buf: Buffer, pos: number) => buf.set(val, pos),
             value.length,
diff --git a/src/schema.ts b/src/schema.ts
index 0e6f7c49d..085438bb7 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -101,12 +101,8 @@ export function generateSchema(ctx: Context, fileDesc: FileDescriptorProto, sour
 
   let fileOptions: Code | undefined;
   if (fileDesc.options) {
-    fileOptions = encodedOptionsToOptions(
-      ctx,
-      ".google.protobuf.FileOptions",
-      (fileDesc.options as any)["_unknownFields"]
-    );
-    delete (fileDesc.options as any)["_unknownFields"];
+    fileOptions = encodedOptionsToOptions(ctx, ".google.protobuf.FileOptions", fileDesc.options._unknownFields);
+    delete fileDesc.options._unknownFields;
   }
 
   const messagesOptions: Code[] = [];
@@ -125,9 +121,9 @@ export function generateSchema(ctx: Context, fileDesc: FileDescriptorProto, sour
         const methodOptions = encodedOptionsToOptions(
           ctx,
           ".google.protobuf.MethodOptions",
-          (method.options as any)["_unknownFields"]
+          method.options._unknownFields
         );
-        delete (method.options as any)["_unknownFields"];
+        delete method.options._unknownFields;
         if (methodOptions) {
           methodsOptions.push(code`'${method.name}': ${methodOptions}`);
         }
@@ -136,12 +132,8 @@ export function generateSchema(ctx: Context, fileDesc: FileDescriptorProto, sour
 
     let serviceOptions: Code | undefined;
     if (service.options) {
-      serviceOptions = encodedOptionsToOptions(
-        ctx,
-        ".google.protobuf.ServiceOptions",
-        (service.options as any)["_unknownFields"]
-      );
-      delete (service.options as any)["_unknownFields"];
+      serviceOptions = encodedOptionsToOptions(ctx, ".google.protobuf.ServiceOptions", service.options._unknownFields);
+      delete service.options._unknownFields;
     }
 
     if (methodsOptions.length > 0 || serviceOptions) {
@@ -162,9 +154,9 @@ export function generateSchema(ctx: Context, fileDesc: FileDescriptorProto, sour
         const valueOptions = encodedOptionsToOptions(
           ctx,
           ".google.protobuf.EnumValueOptions",
-          (value.options as any)["_unknownFields"]
+          value.options._unknownFields
         );
-        delete (value.options as any)["_unknownFields"];
+        delete value.options._unknownFields;
         if (valueOptions) {
           valuesOptions.push(code`'${value.name}': ${valueOptions}`);
         }
@@ -173,12 +165,8 @@ export function generateSchema(ctx: Context, fileDesc: FileDescriptorProto, sour
 
     let enumOptions: Code | undefined;
     if (Enum.options) {
-      enumOptions = encodedOptionsToOptions(
-        ctx,
-        ".google.protobuf.EnumOptions",
-        (Enum.options as any)["_unknownFields"]
-      );
-      delete (Enum.options as any)["_unknownFields"];
+      enumOptions = encodedOptionsToOptions(ctx, ".google.protobuf.EnumOptions", Enum.options._unknownFields);
+      delete Enum.options._unknownFields;
     }
 
     if (valuesOptions.length > 0 || enumOptions) {
@@ -239,13 +227,14 @@ function getExtensionValue(ctx: Context, extension: FieldDescriptorProto, data:
 function encodedOptionsToOptions(
   ctx: Context,
   extendee: string,
-  encodedOptions: { [key: number]: Uint8Array[] }
+  encodedOptions?: { [key: number]: Uint8Array[] }
 ): Code | undefined {
   if (!encodedOptions) {
     return undefined;
   }
   const resultOptions: Code[] = [];
-  for (const [key, value] of Object.entries(encodedOptions)) {
+  for (const key in encodedOptions) {
+    const value = encodedOptions[key];
     const extension = extensionCache[extendee][parseInt(key, 10) >>> 3];
     resultOptions.push(getExtensionValue(ctx, extension, value));
   }
@@ -259,12 +248,8 @@ function resolveMessageOptions(ctx: Context, message: DescriptorProto): Code | u
   const fieldsOptions: Code[] = [];
   message.field.forEach((field) => {
     if (field.options) {
-      const fieldOptions = encodedOptionsToOptions(
-        ctx,
-        ".google.protobuf.FieldOptions",
-        (field.options as any)["_unknownFields"]
-      );
-      delete (field.options as any)["_unknownFields"];
+      const fieldOptions = encodedOptionsToOptions(ctx, ".google.protobuf.FieldOptions", field.options._unknownFields);
+      delete field.options._unknownFields;
       if (fieldOptions) {
         fieldsOptions.push(code`'${field.name}': ${fieldOptions}`);
       }
@@ -274,12 +259,8 @@ function resolveMessageOptions(ctx: Context, message: DescriptorProto): Code | u
   const oneOfsOptions: Code[] = [];
   message.oneofDecl.forEach((oneOf) => {
     if (oneOf.options) {
-      const oneOfOptions = encodedOptionsToOptions(
-        ctx,
-        ".google.protobuf.OneofOptions",
-        (oneOf.options as any)["_unknownFields"]
-      );
-      delete (oneOf.options as any)["_unknownFields"];
+      const oneOfOptions = encodedOptionsToOptions(ctx, ".google.protobuf.OneofOptions", oneOf.options._unknownFields);
+      delete oneOf.options._unknownFields;
       if (oneOfOptions) {
         oneOfsOptions.push(code`'${oneOf.name}': ${oneOfOptions}`);
       }
@@ -298,12 +279,8 @@ function resolveMessageOptions(ctx: Context, message: DescriptorProto): Code | u
 
   let messageOptions: Code | undefined;
   if (message.options) {
-    messageOptions = encodedOptionsToOptions(
-      ctx,
-      ".google.protobuf.MessageOptions",
-      (message.options as any)["_unknownFields"]
-    );
-    delete (message.options as any)["_unknownFields"];
+    messageOptions = encodedOptionsToOptions(ctx, ".google.protobuf.MessageOptions", message.options._unknownFields);
+    delete message.options._unknownFields;
   }
 
   if (fieldsOptions.length > 0 || oneOfsOptions.length > 0 || nestedOptions.length > 0 || messageOptions) {