diff --git a/lib/plugin/utils/plugin-utils.ts b/lib/plugin/utils/plugin-utils.ts
index 2bf55a59b..3608931f3 100644
--- a/lib/plugin/utils/plugin-utils.ts
+++ b/lib/plugin/utils/plugin-utils.ts
@@ -246,7 +246,7 @@ export function isAutoGeneratedEnumUnion(
       return undefined;
     }
     const undefinedTypeIndex = type.types.findIndex(
-      (type: any) => type.intrinsicName === 'undefined'
+      (type: any) => type.intrinsicName === 'undefined' || type.intrinsicName === 'null'
     );
     if (undefinedTypeIndex < 0) {
       return undefined;
diff --git a/test/plugin/fixtures/nullable.dto.ts b/test/plugin/fixtures/nullable.dto.ts
index c94ea4819..86572b2c8 100644
--- a/test/plugin/fixtures/nullable.dto.ts
+++ b/test/plugin/fixtures/nullable.dto.ts
@@ -1,4 +1,8 @@
 export const nullableDtoText = `
+enum OneValueEnum {
+    ONE
+}
+
 export class NullableDto {
   @ApiProperty()
   stringValue: string | null;
@@ -8,13 +12,23 @@ export class NullableDto {
   optionalString?: string;
   @ApiProperty()
   undefinedString: string | undefined;
+  @ApiProperty()
+  nullableEnumValue: OneValueEnum | null;
+  @ApiProperty()
+  optionalEnumValue?: OneValueEnum;
+  @ApiProperty()
+  undefinedEnumValue: OneValueEnum | undefined;
 }
 `;
 
 export const nullableDtoTextTranspiled = `import * as openapi from "@nestjs/swagger";
+var OneValueEnum;
+(function (OneValueEnum) {
+    OneValueEnum[OneValueEnum["ONE"] = 0] = "ONE";
+})(OneValueEnum || (OneValueEnum = {}));
 export class NullableDto {
     static _OPENAPI_METADATA_FACTORY() {
-        return { stringValue: { required: true, type: () => String, nullable: true }, stringArr: { required: true, type: () => [String], nullable: true }, optionalString: { required: false, type: () => String }, undefinedString: { required: true, type: () => String } };
+        return { stringValue: { required: true, type: () => String, nullable: true }, stringArr: { required: true, type: () => [String], nullable: true }, optionalString: { required: false, type: () => String }, undefinedString: { required: true, type: () => String }, nullableEnumValue: { required: true, nullable: true, enum: OneValueEnum }, optionalEnumValue: { required: false, enum: OneValueEnum }, undefinedEnumValue: { required: true, enum: OneValueEnum } };
     }
 }
 __decorate([
@@ -29,4 +43,13 @@ __decorate([
 __decorate([
     ApiProperty()
 ], NullableDto.prototype, "undefinedString", void 0);
+__decorate([
+    ApiProperty()
+], NullableDto.prototype, "nullableEnumValue", void 0);
+__decorate([
+    ApiProperty()
+], NullableDto.prototype, "optionalEnumValue", void 0);
+__decorate([
+    ApiProperty()
+], NullableDto.prototype, "undefinedEnumValue", void 0);
 `;