diff --git a/lib/plugin/utils/plugin-utils.ts b/lib/plugin/utils/plugin-utils.ts
index f68fc4e7f..15db767c4 100644
--- a/lib/plugin/utils/plugin-utils.ts
+++ b/lib/plugin/utils/plugin-utils.ts
@@ -62,11 +62,9 @@ export function getTypeReferenceAsString(
     if (text === Date.name) {
       return text;
     }
-    if (isAutoGeneratedUnion(type)) {
-      return getTypeReferenceAsString(
-        type.types[type.types.length - 1],
-        typeChecker
-      );
+    if (isAutoGeneratedUnion(type, typeChecker)) {
+      const types = (type as ts.UnionOrIntersectionType).types;
+      return getTypeReferenceAsString(types[types.length - 1], typeChecker);
     }
     if (
       text === 'any' ||
@@ -151,13 +149,44 @@ export function isDynamicallyAdded(identifier: ts.Node) {
  * @param type
  */
 export function isAutoGeneratedUnion(
-  type: ts.Type
-): type is ts.UnionOrIntersectionType {
+  type: ts.Type,
+  typeChecker: ts.TypeChecker
+): boolean | ts.Type {
   if (type.isUnionOrIntersection() && !isEnum(type)) {
-    if (type.types && type.types.length === 2) {
-      if (type.types.some((type: any) => type.intrinsicName === 'undefined')) {
+    if (!type.types) {
+      return false;
+    }
+    const undefinedTypeIndex = type.types.findIndex(
+      (type: any) => type.intrinsicName === 'undefined'
+    );
+
+    // "strict" mode for enums
+    let parentType = undefined;
+    const isParentSymbolEqual = type.types.every((item, index) => {
+      if (index === undefinedTypeIndex) {
         return true;
       }
+      if (!item.symbol) {
+        return false;
+      }
+      if (!(item.symbol as any).parent) {
+        return false;
+      }
+      const symbolType = typeChecker.getDeclaredTypeOfSymbol(
+        (item.symbol as any).parent
+      );
+      if (symbolType === parentType || !parentType) {
+        parentType = symbolType;
+        return true;
+      }
+      return false;
+    });
+    if (isParentSymbolEqual) {
+      return parentType;
+    }
+    // "strict" mode for non-enum properties
+    if (type.types.length === 2 && undefinedTypeIndex >= 0) {
+      return true;
     }
   }
   return false;
diff --git a/lib/plugin/visitors/model-class.visitor.ts b/lib/plugin/visitors/model-class.visitor.ts
index 34271fc8a..0466bfc8f 100644
--- a/lib/plugin/visitors/model-class.visitor.ts
+++ b/lib/plugin/visitors/model-class.visitor.ts
@@ -14,6 +14,7 @@ import {
   getDecoratorOrUndefinedByNames,
   getTypeReferenceAsString,
   hasPropertyKey,
+  isAutoGeneratedUnion,
   replaceImportPath
 } from '../utils/plugin-utils';
 import { AbstractFileVisitor } from './abstract.visitor';
@@ -237,7 +238,12 @@ export class ModelClassVisitor extends AbstractFileVisitor {
       }
     }
     if (!isEnum(type)) {
-      return undefined;
+      const typeOrBool = isAutoGeneratedUnion(type, typeChecker);
+      if (typeof typeOrBool !== 'boolean') {
+        type = typeOrBool;
+      } else {
+        return undefined;
+      }
     }
     const enumRef = replaceImportPath(getText(type, typeChecker), hostFilename);
     const enumProperty = ts.createPropertyAssignment(
diff --git a/test/plugin/fixtures/create-cat.dto.ts b/test/plugin/fixtures/create-cat.dto.ts
index 14c67c90c..0a3359d20 100644
--- a/test/plugin/fixtures/create-cat.dto.ts
+++ b/test/plugin/fixtures/create-cat.dto.ts
@@ -17,6 +17,7 @@ export class CreateCatDto {
   age: number = 3;
   tags: string[];
   status: Status = Status.ENABLED;
+  status2?: Status;
 
   @ApiProperty({ type: String })
   @IsString()
@@ -45,7 +46,7 @@ export class CreateCatDto {
         this.status = Status.ENABLED;
     }
     static _OPENAPI_METADATA_FACTORY() {
-        return { name: { required: true, type: () => String }, age: { required: true, type: () => Number, default: 3, minimum: 0, maximum: 10 }, tags: { required: true, type: () => [String] }, status: { required: true, default: Status.ENABLED, enum: Status }, breed: { required: false, type: () => String }, nodes: { required: true, type: () => [Object] }, date: { required: true, type: () => Date } };
+        return { name: { required: true, type: () => String }, age: { required: true, type: () => Number, default: 3, minimum: 0, maximum: 10 }, tags: { required: true, type: () => [String] }, status: { required: true, default: Status.ENABLED, enum: Status }, status2: { required: false, enum: Status }, breed: { required: false, type: () => String }, nodes: { required: true, type: () => [Object] }, date: { required: true, type: () => Date } };
     }
 }
 __decorate([
diff --git a/test/plugin/model-class-visitor.spec.ts b/test/plugin/model-class-visitor.spec.ts
index 5aa317e33..08ad29945 100644
--- a/test/plugin/model-class-visitor.spec.ts
+++ b/test/plugin/model-class-visitor.spec.ts
@@ -23,7 +23,8 @@ describe('API model properties', () => {
       module: ts.ModuleKind.ESNext,
       target: ts.ScriptTarget.ESNext,
       newLine: ts.NewLineKind.LineFeed,
-      noEmitHelpers: true
+      noEmitHelpers: true,
+      strict: true
     };
     const filename = 'create-cat.dto.ts';
     const fakeProgram = ts.createProgram([filename], options);
@@ -43,7 +44,8 @@ describe('API model properties', () => {
       module: ts.ModuleKind.ESNext,
       target: ts.ScriptTarget.ESNext,
       newLine: ts.NewLineKind.LineFeed,
-      noEmitHelpers: true
+      noEmitHelpers: true,
+      strict: true
     };
     const filename = 'create-cat.dto.ts';
     const fakeProgram = ts.createProgram([filename], options);
@@ -63,7 +65,8 @@ describe('API model properties', () => {
       module: ts.ModuleKind.ESNext,
       target: ts.ScriptTarget.ESNext,
       newLine: ts.NewLineKind.LineFeed,
-      noEmitHelpers: true
+      noEmitHelpers: true,
+      strict: true
     };
     const filename = 'create-cat-alt2.dto.ts';
     const fakeProgram = ts.createProgram([filename], options);
@@ -83,7 +86,8 @@ describe('API model properties', () => {
       module: ts.ModuleKind.CommonJS,
       target: ts.ScriptTarget.ES5,
       newLine: ts.NewLineKind.LineFeed,
-      noEmitHelpers: true
+      noEmitHelpers: true,
+      strict: true
     };
     const filename = 'es5-class.dto.ts';
     const fakeProgram = ts.createProgram([filename], options);