diff --git a/integration/grpc-js/google/protobuf/struct.ts b/integration/grpc-js/google/protobuf/struct.ts
index 80a98258e..bdf63bfd3 100644
--- a/integration/grpc-js/google/protobuf/struct.ts
+++ b/integration/grpc-js/google/protobuf/struct.ts
@@ -67,27 +67,27 @@ export interface Struct_FieldsEntry {
  */
 export interface Value {
   /** Represents a null value. */
-  nullValue:
+  nullValue?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  numberValue:
+  numberValue?:
     | number
     | undefined;
   /** Represents a string value. */
-  stringValue:
+  stringValue?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  boolValue:
+  boolValue?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  structValue:
+  structValue?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  listValue: Array<any> | undefined;
+  listValue?: Array<any> | undefined;
 }
 
 /**
diff --git a/integration/meta-typings/simple.ts b/integration/meta-typings/simple.ts
index 78ba9ff31..70dbde53a 100644
--- a/integration/meta-typings/simple.ts
+++ b/integration/meta-typings/simple.ts
@@ -78,8 +78,8 @@ export interface Nested_InnerMessage_DeepMessage {
 }
 
 export interface OneOfMessage {
-  first: string | undefined;
-  last: string | undefined;
+  first?: string | undefined;
+  last?: string | undefined;
 }
 
 export interface SimpleWithWrappers {
diff --git a/integration/nice-grpc/google/protobuf/struct.ts b/integration/nice-grpc/google/protobuf/struct.ts
index 41ef5d717..de3ac954c 100644
--- a/integration/nice-grpc/google/protobuf/struct.ts
+++ b/integration/nice-grpc/google/protobuf/struct.ts
@@ -67,27 +67,27 @@ export interface Struct_FieldsEntry {
  */
 export interface Value {
   /** Represents a null value. */
-  nullValue:
+  nullValue?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  numberValue:
+  numberValue?:
     | number
     | undefined;
   /** Represents a string value. */
-  stringValue:
+  stringValue?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  boolValue:
+  boolValue?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  structValue:
+  structValue?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  listValue: Array<any> | undefined;
+  listValue?: Array<any> | undefined;
 }
 
 /**
diff --git a/integration/oneof-properties/oneof-properties-test.ts b/integration/oneof-properties/oneof-properties-test.ts
index 50a3ed74b..d52f50697 100644
--- a/integration/oneof-properties/oneof-properties-test.ts
+++ b/integration/oneof-properties/oneof-properties-test.ts
@@ -161,4 +161,12 @@ describe('oneof=properties (default)', () => {
     let fromJson = PleaseChoose.fromJSON(pbjsJson);
     expect(fromJson).toEqual(debbie);
   });
+
+  it('should allow to omit oneOf fields', () => {
+    const msg: PleaseChoose = {
+       name: 'foo',
+       age: 42,
+    };
+    expect(msg).toBeDefined();
+  });
 });
diff --git a/integration/oneof-properties/oneof.ts b/integration/oneof-properties/oneof.ts
index a80318c1d..d371b089d 100644
--- a/integration/oneof-properties/oneof.ts
+++ b/integration/oneof-properties/oneof.ts
@@ -9,28 +9,28 @@ export interface PleaseChoose {
    * Use this if you want a number. Numbers are great. Who doesn't
    * like them?
    */
-  aNumber:
+  aNumber?:
     | number
     | undefined;
   /**
    * Use this if you want a string. Strings are also nice. Not as
    * nice as numbers, but what are you going to do...
    */
-  aString: string | undefined;
-  aMessage:
+  aString?: string | undefined;
+  aMessage?:
     | PleaseChoose_Submessage
     | undefined;
   /**
    * We also added a bool option! This was added after the 'age'
    * field, so it has a higher number.
    */
-  aBool: boolean | undefined;
-  bunchaBytes: Uint8Array | undefined;
-  anEnum: PleaseChoose_StateEnum | undefined;
+  aBool?: boolean | undefined;
+  bunchaBytes?: Uint8Array | undefined;
+  anEnum?: PleaseChoose_StateEnum | undefined;
   age: number;
-  either: string | undefined;
-  or: string | undefined;
-  thirdOption: string | undefined;
+  either?: string | undefined;
+  or?: string | undefined;
+  thirdOption?: string | undefined;
 }
 
 export enum PleaseChoose_StateEnum {
diff --git a/integration/options/options.ts b/integration/options/options.ts
index 4cae7acd2..f0b907540 100644
--- a/integration/options/options.ts
+++ b/integration/options/options.ts
@@ -16,7 +16,7 @@ export interface MyMessage {
   foo?: number | undefined;
   foo2?: number | undefined;
   bar?: string | undefined;
-  quux: string | undefined;
+  quux?: string | undefined;
 }
 
 export interface RequestType {
diff --git a/integration/simple-optionals/simple.ts b/integration/simple-optionals/simple.ts
index b9057e316..d3e4dfd82 100644
--- a/integration/simple-optionals/simple.ts
+++ b/integration/simple-optionals/simple.ts
@@ -169,8 +169,8 @@ export interface Nested_InnerMessage_DeepMessage {
 }
 
 export interface OneOfMessage {
-  first: string | undefined;
-  last: string | undefined;
+  first?: string | undefined;
+  last?: string | undefined;
 }
 
 export interface SimpleWithWrappers {
diff --git a/integration/simple-prototype-defaults/simple.ts b/integration/simple-prototype-defaults/simple.ts
index 57f940fdf..6671674e5 100644
--- a/integration/simple-prototype-defaults/simple.ts
+++ b/integration/simple-prototype-defaults/simple.ts
@@ -173,8 +173,8 @@ export interface Nested_InnerMessage_DeepMessage {
 }
 
 export interface OneOfMessage {
-  first: string | undefined;
-  last: string | undefined;
+  first?: string | undefined;
+  last?: string | undefined;
 }
 
 export interface SimpleWithWrappers {
diff --git a/integration/simple-snake/google/protobuf/struct.ts b/integration/simple-snake/google/protobuf/struct.ts
index 802676863..94feaf5b2 100644
--- a/integration/simple-snake/google/protobuf/struct.ts
+++ b/integration/simple-snake/google/protobuf/struct.ts
@@ -67,27 +67,27 @@ export interface Struct_FieldsEntry {
  */
 export interface Value {
   /** Represents a null value. */
-  null_value:
+  null_value?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  number_value:
+  number_value?:
     | number
     | undefined;
   /** Represents a string value. */
-  string_value:
+  string_value?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  bool_value:
+  bool_value?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  struct_value:
+  struct_value?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  list_value: Array<any> | undefined;
+  list_value?: Array<any> | undefined;
 }
 
 /**
diff --git a/integration/simple-snake/simple.ts b/integration/simple-snake/simple.ts
index 68f20abca..5d416272c 100644
--- a/integration/simple-snake/simple.ts
+++ b/integration/simple-snake/simple.ts
@@ -170,8 +170,8 @@ export interface Nested_InnerMessage_DeepMessage {
 }
 
 export interface OneOfMessage {
-  first: string | undefined;
-  last: string | undefined;
+  first?: string | undefined;
+  last?: string | undefined;
 }
 
 export interface SimpleWithWrappers {
diff --git a/integration/simple-string-enums/google/protobuf/struct.ts b/integration/simple-string-enums/google/protobuf/struct.ts
index 4e88bc237..dfc921bd5 100644
--- a/integration/simple-string-enums/google/protobuf/struct.ts
+++ b/integration/simple-string-enums/google/protobuf/struct.ts
@@ -77,27 +77,27 @@ export interface Struct_FieldsEntry {
  */
 export interface Value {
   /** Represents a null value. */
-  nullValue:
+  nullValue?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  numberValue:
+  numberValue?:
     | number
     | undefined;
   /** Represents a string value. */
-  stringValue:
+  stringValue?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  boolValue:
+  boolValue?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  structValue:
+  structValue?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  listValue: Array<any> | undefined;
+  listValue?: Array<any> | undefined;
 }
 
 /**
diff --git a/integration/simple-unrecognized-enum/simple.ts b/integration/simple-unrecognized-enum/simple.ts
index 708c09602..e0a1ad32a 100644
--- a/integration/simple-unrecognized-enum/simple.ts
+++ b/integration/simple-unrecognized-enum/simple.ts
@@ -157,8 +157,8 @@ export interface Nested_InnerMessage_DeepMessage {
 }
 
 export interface OneOfMessage {
-  first: string | undefined;
-  last: string | undefined;
+  first?: string | undefined;
+  last?: string | undefined;
 }
 
 export interface SimpleWithWrappers {
diff --git a/integration/simple/simple.ts b/integration/simple/simple.ts
index 696e581cf..b0881b28b 100644
--- a/integration/simple/simple.ts
+++ b/integration/simple/simple.ts
@@ -174,8 +174,8 @@ export interface Nested_InnerMessage_DeepMessage {
 }
 
 export interface OneOfMessage {
-  first: string | undefined;
-  last: string | undefined;
+  first?: string | undefined;
+  last?: string | undefined;
 }
 
 export interface SimpleWithWrappers {
diff --git a/integration/struct/google/protobuf/struct.ts b/integration/struct/google/protobuf/struct.ts
index 80a98258e..bdf63bfd3 100644
--- a/integration/struct/google/protobuf/struct.ts
+++ b/integration/struct/google/protobuf/struct.ts
@@ -67,27 +67,27 @@ export interface Struct_FieldsEntry {
  */
 export interface Value {
   /** Represents a null value. */
-  nullValue:
+  nullValue?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  numberValue:
+  numberValue?:
     | number
     | undefined;
   /** Represents a string value. */
-  stringValue:
+  stringValue?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  boolValue:
+  boolValue?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  structValue:
+  structValue?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  listValue: Array<any> | undefined;
+  listValue?: Array<any> | undefined;
 }
 
 /**
diff --git a/integration/type-registry/google/protobuf/struct.ts b/integration/type-registry/google/protobuf/struct.ts
index 6f035c984..957a66993 100644
--- a/integration/type-registry/google/protobuf/struct.ts
+++ b/integration/type-registry/google/protobuf/struct.ts
@@ -71,27 +71,27 @@ export interface Struct_FieldsEntry {
 export interface Value {
   $type: "google.protobuf.Value";
   /** Represents a null value. */
-  nullValue:
+  nullValue?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  numberValue:
+  numberValue?:
     | number
     | undefined;
   /** Represents a string value. */
-  stringValue:
+  stringValue?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  boolValue:
+  boolValue?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  structValue:
+  structValue?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  listValue: Array<any> | undefined;
+  listValue?: Array<any> | undefined;
 }
 
 /**
diff --git a/integration/types-with-underscores/file.ts b/integration/types-with-underscores/file.ts
index f8764f977..391d5bce2 100644
--- a/integration/types-with-underscores/file.ts
+++ b/integration/types-with-underscores/file.ts
@@ -4,7 +4,7 @@ import * as _m0 from "protobufjs/minimal";
 export const protobufPackage = "";
 
 export interface Baz {
-  foo: FooBar | undefined;
+  foo?: FooBar | undefined;
 }
 
 export interface FooBar {
diff --git a/integration/unknown-fields/options.ts b/integration/unknown-fields/options.ts
index 8f9c57745..f56eae9a9 100644
--- a/integration/unknown-fields/options.ts
+++ b/integration/unknown-fields/options.ts
@@ -13,7 +13,7 @@ export interface MyMessage {
   foo?: number | undefined;
   foo2?: number | undefined;
   bar?: string | undefined;
-  quux: string | undefined;
+  quux?: string | undefined;
 }
 
 export interface RequestType {
diff --git a/integration/use-numeric-enum-json/google/protobuf/struct.ts b/integration/use-numeric-enum-json/google/protobuf/struct.ts
index d17382273..8b67dc03d 100644
--- a/integration/use-numeric-enum-json/google/protobuf/struct.ts
+++ b/integration/use-numeric-enum-json/google/protobuf/struct.ts
@@ -67,27 +67,27 @@ export interface Struct_FieldsEntry {
  */
 export interface Value {
   /** Represents a null value. */
-  nullValue:
+  nullValue?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  numberValue:
+  numberValue?:
     | number
     | undefined;
   /** Represents a string value. */
-  stringValue:
+  stringValue?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  boolValue:
+  boolValue?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  structValue:
+  structValue?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  listValue: Array<any> | undefined;
+  listValue?: Array<any> | undefined;
 }
 
 /**
diff --git a/integration/value/google/protobuf/struct.ts b/integration/value/google/protobuf/struct.ts
index 80a98258e..bdf63bfd3 100644
--- a/integration/value/google/protobuf/struct.ts
+++ b/integration/value/google/protobuf/struct.ts
@@ -67,27 +67,27 @@ export interface Struct_FieldsEntry {
  */
 export interface Value {
   /** Represents a null value. */
-  nullValue:
+  nullValue?:
     | NullValue
     | undefined;
   /** Represents a double value. */
-  numberValue:
+  numberValue?:
     | number
     | undefined;
   /** Represents a string value. */
-  stringValue:
+  stringValue?:
     | string
     | undefined;
   /** Represents a boolean value. */
-  boolValue:
+  boolValue?:
     | boolean
     | undefined;
   /** Represents a structured value. */
-  structValue:
+  structValue?:
     | { [key: string]: any }
     | undefined;
   /** Represents a repeated `Value`. */
-  listValue: Array<any> | undefined;
+  listValue?: Array<any> | undefined;
 }
 
 /**
diff --git a/src/types.ts b/src/types.ts
index 65b6df404..537a6e6e3 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -337,6 +337,7 @@ export function isScalar(field: FieldDescriptorProto): boolean {
 // properties. When useOptionals='all', all fields are translated into
 // optional properties, with the exception of map Entry key/values, which must
 // always be present.
+// OneOf fields are always optional, whenever oneof=unions option not in use.
 export function isOptionalProperty(
   field: FieldDescriptorProto,
   messageOptions: MessageOptions | undefined,
@@ -348,6 +349,8 @@ export function isOptionalProperty(
   return (
     (optionalMessages && isMessage(field) && !isRepeated(field)) ||
     (optionalAll && !messageOptions?.mapEntry) ||
+    // don't bother verifying that oneof is not union. union oneofs generate their own properties.
+    isWithinOneOf(field) ||
     field.proto3Optional
   );
 }