diff --git a/integration/oneof-unions/oneof-unions-test.ts b/integration/oneof-unions/oneof-unions-test.ts
index 6cdc2f11d..65ee9b6ed 100644
--- a/integration/oneof-unions/oneof-unions-test.ts
+++ b/integration/oneof-unions/oneof-unions-test.ts
@@ -3,12 +3,22 @@ import { PleaseChoose } from './oneof';
 
 describe('oneof=unions', () => {
   it('generates types correctly', () => {
-    const alice: PleaseChoose = { name: 'Alice', age: 42 };
-    const bob: PleaseChoose = { name: 'Bob', age: 42, choice: { $case: 'aNumber', aNumber: 132 } };
+    const alice: PleaseChoose = {
+      name: 'Alice',
+      age: 42,
+      signature: new Uint8Array([0xab, 0xcd]),
+    };
+    const bob: PleaseChoose = {
+      name: 'Bob',
+      age: 42,
+      choice: { $case: 'aNumber', aNumber: 132 },
+      signature: new Uint8Array([0xab, 0xcd]),
+    };
     const charlie: PleaseChoose = {
       name: 'Charlie',
       age: 42,
       choice: { $case: 'aMessage', aMessage: { name: 'charlie' } },
+      signature: new Uint8Array([0xab, 0xcd]),
     };
   });
 
@@ -27,6 +37,7 @@ describe('oneof=unions', () => {
       age: 37,
       choice: { $case: 'aBool', aBool: true },
       eitherOr: { $case: 'or', or: 'perhaps not' },
+      signature: new Uint8Array(),
     });
   });
 
@@ -36,6 +47,7 @@ describe('oneof=unions', () => {
       age: 37,
       choice: { $case: 'aBool', aBool: true },
       eitherOr: { $case: 'or', or: 'perhaps not' },
+      signature: new Uint8Array([0xab, 0xcd]),
     }).finish();
     let decoded = pbjs.PleaseChoose.decode(encoded);
     expect(decoded).toEqual({
@@ -43,6 +55,7 @@ describe('oneof=unions', () => {
       aBool: true,
       age: 37,
       or: 'perhaps not',
+      signature: Buffer.from([0xab, 0xcd]),
     });
   });
 
@@ -51,6 +64,7 @@ describe('oneof=unions', () => {
     expect(empty).toEqual({
       name: '',
       age: 0,
+      signature: new Uint8Array(),
     });
 
     let partial = PleaseChoose.fromPartial({
@@ -58,12 +72,14 @@ describe('oneof=unions', () => {
       age: 37,
       choice: { $case: 'aBool', aBool: true },
       eitherOr: { $case: 'or', or: 'perhaps not' },
+      signature: new Uint8Array([0xab, 0xcd]),
     });
     expect(partial).toEqual({
       name: 'Debbie',
       age: 37,
       choice: { $case: 'aBool', aBool: true },
       eitherOr: { $case: 'or', or: 'perhaps not' },
+      signature: new Uint8Array([0xab, 0xcd]),
     });
   });
 
@@ -73,6 +89,7 @@ describe('oneof=unions', () => {
       age: 37,
       choice: { $case: 'aBool', aBool: true },
       eitherOr: { $case: 'or', or: 'perhaps not' },
+      signature: new Uint8Array([0xab, 0xcd]),
     };
     let pbjsJson = pbjs.PleaseChoose.decode(PleaseChoose.encode(debbie).finish()).toJSON();
     let json = PleaseChoose.toJSON(debbie);
@@ -81,13 +98,14 @@ describe('oneof=unions', () => {
 
   it('fromJSON', () => {
     let empty = PleaseChoose.fromJSON({});
-    expect(empty).toEqual({ age: 0, name: '' });
+    expect(empty).toEqual({ age: 0, name: '', signature: new Uint8Array() });
 
     let debbie: PleaseChoose = {
       name: 'Debbie',
       age: 37,
       choice: { $case: 'aBool', aBool: true },
       eitherOr: { $case: 'or', or: 'perhaps not' },
+      signature: new Uint8Array([0xab, 0xcd]),
     };
     let pbjsJson = pbjs.PleaseChoose.decode(PleaseChoose.encode(debbie).finish()).toJSON();
     let fromJson = PleaseChoose.fromJSON(pbjsJson);
@@ -99,6 +117,7 @@ describe('oneof=unions', () => {
       name: 'Debbie',
       age: 37,
       choice: { $case: 'aNumber', aNumber: 42 },
+      signature: Buffer.from([0xab, 0xcd]),
     };
     let encoded = PleaseChoose.encode(obj).finish();
     let decoded = PleaseChoose.decode(encoded);
diff --git a/integration/oneof-unions/oneof.bin b/integration/oneof-unions/oneof.bin
index 45b7fdb4f..365dbb4d0 100644
Binary files a/integration/oneof-unions/oneof.bin and b/integration/oneof-unions/oneof.bin differ
diff --git a/integration/oneof-unions/oneof.proto b/integration/oneof-unions/oneof.proto
index cf0a4fe45..1f8a35697 100644
--- a/integration/oneof-unions/oneof.proto
+++ b/integration/oneof-unions/oneof.proto
@@ -46,6 +46,7 @@ message PleaseChoose {
     string third_option = 9;
   }
 
+  bytes signature = 12;
 }
 
 /** For testing proto3's field presence feature. */
diff --git a/integration/oneof-unions/oneof.ts b/integration/oneof-unions/oneof.ts
index fd55ba7be..4f419f7fd 100644
--- a/integration/oneof-unions/oneof.ts
+++ b/integration/oneof-unions/oneof.ts
@@ -18,6 +18,7 @@ export interface PleaseChoose {
     | { $case: 'either'; either: string }
     | { $case: 'or'; or: string }
     | { $case: 'thirdOption'; thirdOption: string };
+  signature: Uint8Array;
 }
 
 export enum PleaseChoose_StateEnum {
@@ -105,6 +106,9 @@ export const PleaseChoose = {
     if (message.eitherOr?.$case === 'thirdOption') {
       writer.uint32(74).string(message.eitherOr.thirdOption);
     }
+    if (message.signature.length !== 0) {
+      writer.uint32(98).bytes(message.signature);
+    }
     return writer;
   },
 
@@ -112,6 +116,7 @@ export const PleaseChoose = {
     const reader = input instanceof Reader ? input : new Reader(input);
     let end = length === undefined ? reader.len : reader.pos + length;
     const message = { ...basePleaseChoose } as PleaseChoose;
+    message.signature = new Uint8Array();
     while (reader.pos < end) {
       const tag = reader.uint32();
       switch (tag >>> 3) {
@@ -148,6 +153,9 @@ export const PleaseChoose = {
         case 9:
           message.eitherOr = { $case: 'thirdOption', thirdOption: reader.string() };
           break;
+        case 12:
+          message.signature = reader.bytes();
+          break;
         default:
           reader.skipType(tag & 7);
           break;
@@ -158,6 +166,7 @@ export const PleaseChoose = {
 
   fromJSON(object: any): PleaseChoose {
     const message = { ...basePleaseChoose } as PleaseChoose;
+    message.signature = new Uint8Array();
     if (object.name !== undefined && object.name !== null) {
       message.name = String(object.name);
     }
@@ -191,6 +200,9 @@ export const PleaseChoose = {
     if (object.thirdOption !== undefined && object.thirdOption !== null) {
       message.eitherOr = { $case: 'thirdOption', thirdOption: String(object.thirdOption) };
     }
+    if (object.signature !== undefined && object.signature !== null) {
+      message.signature = bytesFromBase64(object.signature);
+    }
     return message;
   },
 
@@ -212,6 +224,8 @@ export const PleaseChoose = {
     message.eitherOr?.$case === 'either' && (obj.either = message.eitherOr?.either);
     message.eitherOr?.$case === 'or' && (obj.or = message.eitherOr?.or);
     message.eitherOr?.$case === 'thirdOption' && (obj.thirdOption = message.eitherOr?.thirdOption);
+    message.signature !== undefined &&
+      (obj.signature = base64FromBytes(message.signature !== undefined ? message.signature : new Uint8Array()));
     return obj;
   },
 
@@ -219,6 +233,8 @@ export const PleaseChoose = {
     const message = { ...basePleaseChoose } as PleaseChoose;
     if (object.name !== undefined && object.name !== null) {
       message.name = object.name;
+    } else {
+      message.name = '';
     }
     if (object.choice?.$case === 'aNumber' && object.choice?.aNumber !== undefined && object.choice?.aNumber !== null) {
       message.choice = { $case: 'aNumber', aNumber: object.choice.aNumber };
@@ -248,6 +264,8 @@ export const PleaseChoose = {
     }
     if (object.age !== undefined && object.age !== null) {
       message.age = object.age;
+    } else {
+      message.age = 0;
     }
     if (
       object.eitherOr?.$case === 'either' &&
@@ -266,6 +284,11 @@ export const PleaseChoose = {
     ) {
       message.eitherOr = { $case: 'thirdOption', thirdOption: object.eitherOr.thirdOption };
     }
+    if (object.signature !== undefined && object.signature !== null) {
+      message.signature = object.signature;
+    } else {
+      message.signature = new Uint8Array();
+    }
     return message;
   },
 };
@@ -316,6 +339,8 @@ export const PleaseChoose_Submessage = {
     const message = { ...basePleaseChoose_Submessage } as PleaseChoose_Submessage;
     if (object.name !== undefined && object.name !== null) {
       message.name = object.name;
+    } else {
+      message.name = '';
     }
     return message;
   },
@@ -377,9 +402,13 @@ export const SimpleButOptional = {
     const message = { ...baseSimpleButOptional } as SimpleButOptional;
     if (object.name !== undefined && object.name !== null) {
       message.name = object.name;
+    } else {
+      message.name = undefined;
     }
     if (object.age !== undefined && object.age !== null) {
       message.age = object.age;
+    } else {
+      message.age = undefined;
     }
     return message;
   },
diff --git a/src/main.ts b/src/main.ts
index f99a46259..02faa1390 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1222,7 +1222,7 @@ function generateFromPartial(ctx: Context, fullName: string, messageDesc: Descri
       }
     }
 
-    if (!isRepeated(field) && options.oneof !== OneofOption.UNIONS) {
+    if (!isRepeated(field) && !isWithinOneOfThatShouldBeUnion(options, field)) {
       chunks.push(code`} else {`);
       const v = isWithinOneOf(field) ? 'undefined' : defaultValue(ctx, field);
       chunks.push(code`message.${fieldName} = ${v}`);