diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 6dc4ba31b9c..603f45cbf07 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -18717,7 +18717,10 @@ namespace ts {
          * marked as referenced to prevent import elision.
          */
         function markTypeNodeAsReferenced(node: TypeNode) {
-            const typeName = node && getEntityNameFromTypeNode(node);
+            markEntityNameOrEntityExpressionAsReference(node && getEntityNameFromTypeNode(node));
+        }
+
+        function markEntityNameOrEntityExpressionAsReference(typeName: EntityNameOrEntityNameExpression) {
             const rootName = typeName && getFirstIdentifier(typeName);
             const rootSymbol = rootName && resolveName(rootName, rootName.text, (typeName.kind === SyntaxKind.Identifier ? SymbolFlags.Type : SymbolFlags.Namespace) | SymbolFlags.Alias, /*nameNotFoundMessage*/ undefined, /*nameArg*/ undefined);
             if (rootSymbol
@@ -18728,6 +18731,61 @@ namespace ts {
             }
         }
 
+        /**
+         * This function marks the type used for metadata decorator as referenced if it is import
+         * from external module.
+         * This is different from markTypeNodeAsReferenced because it tries to simplify type nodes in
+         * union and intersection type
+         * @param node
+         */
+        function markDecoratorMedataDataTypeNodeAsReferenced(node: TypeNode): void {
+            const entityName = getEntityNameForDecoratorMetadata(node);
+            if (entityName && isEntityName(entityName)) {
+                markEntityNameOrEntityExpressionAsReference(entityName);
+            }
+        }
+
+        function getEntityNameForDecoratorMetadata(node: TypeNode): EntityName {
+            if (node) {
+                switch (node.kind) {
+                    case SyntaxKind.IntersectionType:
+                    case SyntaxKind.UnionType:
+                        let commonEntityName: EntityName;
+                        for (const typeNode of (<UnionOrIntersectionTypeNode>node).types) {
+                            const individualEntityName = getEntityNameForDecoratorMetadata(typeNode);
+                            if (!individualEntityName) {
+                                // Individual is something like string number
+                                // So it would be serialized to either that type or object
+                                // Safe to return here
+                                return undefined;
+                            }
+
+                            if (commonEntityName) {
+                                // Note this is in sync with the transformation that happens for type node.
+                                // Keep this in sync with serializeUnionOrIntersectionType
+                                // Verify if they refer to same entity and is identifier
+                                // return undefined if they dont match because we would emit object
+                                if (!isIdentifier(commonEntityName) ||
+                                    !isIdentifier(individualEntityName) ||
+                                    commonEntityName.text !== individualEntityName.text) {
+                                    return undefined;
+                                }
+                            }
+                            else {
+                                commonEntityName = individualEntityName;
+                            }
+                        }
+                        return commonEntityName;
+
+                    case SyntaxKind.ParenthesizedType:
+                        return getEntityNameForDecoratorMetadata((<ParenthesizedTypeNode>node).type);
+
+                    case SyntaxKind.TypeReference:
+                        return (<TypeReferenceNode>node).typeName;
+                }
+            }
+        }
+
         function getParameterTypeNodeForDecoratorCheck(node: ParameterDeclaration): TypeNode {
             return node.dotDotDotToken ? getRestParameterElementType(node.type) : node.type;
         }
@@ -18763,7 +18821,7 @@ namespace ts {
                         const constructor = getFirstConstructorWithBody(<ClassDeclaration>node);
                         if (constructor) {
                             for (const parameter of constructor.parameters) {
-                                markTypeNodeAsReferenced(getParameterTypeNodeForDecoratorCheck(parameter));
+                                markDecoratorMedataDataTypeNodeAsReferenced(getParameterTypeNodeForDecoratorCheck(parameter));
                             }
                         }
                         break;
@@ -18772,17 +18830,17 @@ namespace ts {
                     case SyntaxKind.GetAccessor:
                     case SyntaxKind.SetAccessor:
                         for (const parameter of (<FunctionLikeDeclaration>node).parameters) {
-                            markTypeNodeAsReferenced(getParameterTypeNodeForDecoratorCheck(parameter));
+                            markDecoratorMedataDataTypeNodeAsReferenced(getParameterTypeNodeForDecoratorCheck(parameter));
                         }
 
-                        markTypeNodeAsReferenced((<FunctionLikeDeclaration>node).type);
+                        markDecoratorMedataDataTypeNodeAsReferenced((<FunctionLikeDeclaration>node).type);
                         break;
 
                     case SyntaxKind.PropertyDeclaration:
-                        markTypeNodeAsReferenced(getParameterTypeNodeForDecoratorCheck(<ParameterDeclaration>node));
+                        markDecoratorMedataDataTypeNodeAsReferenced(getParameterTypeNodeForDecoratorCheck(<ParameterDeclaration>node));
                         break;
                     case SyntaxKind.Parameter:
-                        markTypeNodeAsReferenced((<PropertyDeclaration>node).type);
+                        markDecoratorMedataDataTypeNodeAsReferenced((<PropertyDeclaration>node).type);
                         break;
                 }
             }
diff --git a/src/compiler/transformers/ts.ts b/src/compiler/transformers/ts.ts
index 555855b5e23..f831a09ac6f 100644
--- a/src/compiler/transformers/ts.ts
+++ b/src/compiler/transformers/ts.ts
@@ -1762,23 +1762,19 @@ namespace ts {
         }
 
         function serializeUnionOrIntersectionType(node: UnionOrIntersectionTypeNode): SerializedTypeNode {
+            // Note when updating logic here also update getEntityNameForDecoratorMetadata
+            // so that aliases can be marked as referenced
             let serializedUnion: SerializedTypeNode;
             for (const typeNode of node.types) {
                 const serializedIndividual = serializeTypeNode(typeNode);
 
-                if (isVoidExpression(serializedIndividual)) {
-                    // If we dont have any other type already set, set the initial type
-                    if (!serializedUnion) {
-                        serializedUnion = serializedIndividual;
-                    }
-                }
-                else if (isIdentifier(serializedIndividual) && serializedIndividual.text === "Object") {
+                if (isIdentifier(serializedIndividual) && serializedIndividual.text === "Object") {
                     // One of the individual is global object, return immediately
                     return serializedIndividual;
                 }
                 // If there exists union that is not void 0 expression, check if the the common type is identifier.
                 // anything more complex and we will just default to Object
-                else if (serializedUnion && !isVoidExpression(serializedUnion)) {
+                else if (serializedUnion) {
                     // Different types
                     if (!isIdentifier(serializedUnion) ||
                         !isIdentifier(serializedIndividual) ||
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index e81d57a7df4..f1b181a03b0 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -3574,10 +3574,6 @@ namespace ts {
         return node.kind === SyntaxKind.Identifier;
     }
 
-    export function isVoidExpression(node: Node): node is VoidExpression {
-        return node.kind === SyntaxKind.VoidExpression;
-    }
-
     export function isGeneratedIdentifier(node: Node): node is GeneratedIdentifier {
         // Using `>` here catches both `GeneratedIdentifierKind.None` and `undefined`.
         return isIdentifier(node) && node.autoGenerateKind > GeneratedIdentifierKind.None;
diff --git a/tests/baselines/reference/metadataOfClassFromAlias.js b/tests/baselines/reference/metadataOfClassFromAlias.js
new file mode 100644
index 00000000000..c99f7cc2e23
--- /dev/null
+++ b/tests/baselines/reference/metadataOfClassFromAlias.js
@@ -0,0 +1,50 @@
+//// [tests/cases/compiler/metadataOfClassFromAlias.ts] ////
+
+//// [auxiliry.ts]
+export class SomeClass {
+    field: string;
+}
+
+//// [test.ts]
+import { SomeClass } from './auxiliry';
+function annotation(): PropertyDecorator {
+    return (target: any): void => { };
+}
+export class ClassA {
+    @annotation() array: SomeClass | null;
+}
+
+//// [auxiliry.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+var SomeClass = (function () {
+    function SomeClass() {
+    }
+    return SomeClass;
+}());
+exports.SomeClass = SomeClass;
+//// [test.js]
+"use strict";
+var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
+    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
+    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
+    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
+    return c > 3 && r && Object.defineProperty(target, key, r), r;
+};
+var __metadata = (this && this.__metadata) || function (k, v) {
+    if (typeof Reflect === "object" && typeof Reflect.metadata === "function") return Reflect.metadata(k, v);
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+function annotation() {
+    return function (target) { };
+}
+var ClassA = (function () {
+    function ClassA() {
+    }
+    return ClassA;
+}());
+__decorate([
+    annotation(),
+    __metadata("design:type", Object)
+], ClassA.prototype, "array", void 0);
+exports.ClassA = ClassA;
diff --git a/tests/baselines/reference/metadataOfClassFromAlias.symbols b/tests/baselines/reference/metadataOfClassFromAlias.symbols
new file mode 100644
index 00000000000..b4d20403275
--- /dev/null
+++ b/tests/baselines/reference/metadataOfClassFromAlias.symbols
@@ -0,0 +1,27 @@
+=== tests/cases/compiler/auxiliry.ts ===
+export class SomeClass {
+>SomeClass : Symbol(SomeClass, Decl(auxiliry.ts, 0, 0))
+
+    field: string;
+>field : Symbol(SomeClass.field, Decl(auxiliry.ts, 0, 24))
+}
+
+=== tests/cases/compiler/test.ts ===
+import { SomeClass } from './auxiliry';
+>SomeClass : Symbol(SomeClass, Decl(test.ts, 0, 8))
+
+function annotation(): PropertyDecorator {
+>annotation : Symbol(annotation, Decl(test.ts, 0, 39))
+>PropertyDecorator : Symbol(PropertyDecorator, Decl(lib.d.ts, --, --))
+
+    return (target: any): void => { };
+>target : Symbol(target, Decl(test.ts, 2, 12))
+}
+export class ClassA {
+>ClassA : Symbol(ClassA, Decl(test.ts, 3, 1))
+
+    @annotation() array: SomeClass | null;
+>annotation : Symbol(annotation, Decl(test.ts, 0, 39))
+>array : Symbol(ClassA.array, Decl(test.ts, 4, 21))
+>SomeClass : Symbol(SomeClass, Decl(test.ts, 0, 8))
+}
diff --git a/tests/baselines/reference/metadataOfClassFromAlias.types b/tests/baselines/reference/metadataOfClassFromAlias.types
new file mode 100644
index 00000000000..a14f72ee619
--- /dev/null
+++ b/tests/baselines/reference/metadataOfClassFromAlias.types
@@ -0,0 +1,30 @@
+=== tests/cases/compiler/auxiliry.ts ===
+export class SomeClass {
+>SomeClass : SomeClass
+
+    field: string;
+>field : string
+}
+
+=== tests/cases/compiler/test.ts ===
+import { SomeClass } from './auxiliry';
+>SomeClass : typeof SomeClass
+
+function annotation(): PropertyDecorator {
+>annotation : () => PropertyDecorator
+>PropertyDecorator : PropertyDecorator
+
+    return (target: any): void => { };
+>(target: any): void => { } : (target: any) => void
+>target : any
+}
+export class ClassA {
+>ClassA : ClassA
+
+    @annotation() array: SomeClass | null;
+>annotation() : PropertyDecorator
+>annotation : () => PropertyDecorator
+>array : SomeClass
+>SomeClass : SomeClass
+>null : null
+}
diff --git a/tests/baselines/reference/metadataOfClassFromAlias2.js b/tests/baselines/reference/metadataOfClassFromAlias2.js
new file mode 100644
index 00000000000..bcdbb34ac50
--- /dev/null
+++ b/tests/baselines/reference/metadataOfClassFromAlias2.js
@@ -0,0 +1,50 @@
+//// [tests/cases/compiler/metadataOfClassFromAlias2.ts] ////
+
+//// [auxiliry.ts]
+export class SomeClass {
+    field: string;
+}
+
+//// [test.ts]
+import { SomeClass } from './auxiliry';
+function annotation(): PropertyDecorator {
+    return (target: any): void => { };
+}
+export class ClassA {
+    @annotation() array: SomeClass | null | string;
+}
+
+//// [auxiliry.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+var SomeClass = (function () {
+    function SomeClass() {
+    }
+    return SomeClass;
+}());
+exports.SomeClass = SomeClass;
+//// [test.js]
+"use strict";
+var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
+    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
+    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
+    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
+    return c > 3 && r && Object.defineProperty(target, key, r), r;
+};
+var __metadata = (this && this.__metadata) || function (k, v) {
+    if (typeof Reflect === "object" && typeof Reflect.metadata === "function") return Reflect.metadata(k, v);
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+function annotation() {
+    return function (target) { };
+}
+var ClassA = (function () {
+    function ClassA() {
+    }
+    return ClassA;
+}());
+__decorate([
+    annotation(),
+    __metadata("design:type", Object)
+], ClassA.prototype, "array", void 0);
+exports.ClassA = ClassA;
diff --git a/tests/baselines/reference/metadataOfClassFromAlias2.symbols b/tests/baselines/reference/metadataOfClassFromAlias2.symbols
new file mode 100644
index 00000000000..a20296c76af
--- /dev/null
+++ b/tests/baselines/reference/metadataOfClassFromAlias2.symbols
@@ -0,0 +1,27 @@
+=== tests/cases/compiler/auxiliry.ts ===
+export class SomeClass {
+>SomeClass : Symbol(SomeClass, Decl(auxiliry.ts, 0, 0))
+
+    field: string;
+>field : Symbol(SomeClass.field, Decl(auxiliry.ts, 0, 24))
+}
+
+=== tests/cases/compiler/test.ts ===
+import { SomeClass } from './auxiliry';
+>SomeClass : Symbol(SomeClass, Decl(test.ts, 0, 8))
+
+function annotation(): PropertyDecorator {
+>annotation : Symbol(annotation, Decl(test.ts, 0, 39))
+>PropertyDecorator : Symbol(PropertyDecorator, Decl(lib.d.ts, --, --))
+
+    return (target: any): void => { };
+>target : Symbol(target, Decl(test.ts, 2, 12))
+}
+export class ClassA {
+>ClassA : Symbol(ClassA, Decl(test.ts, 3, 1))
+
+    @annotation() array: SomeClass | null | string;
+>annotation : Symbol(annotation, Decl(test.ts, 0, 39))
+>array : Symbol(ClassA.array, Decl(test.ts, 4, 21))
+>SomeClass : Symbol(SomeClass, Decl(test.ts, 0, 8))
+}
diff --git a/tests/baselines/reference/metadataOfClassFromAlias2.types b/tests/baselines/reference/metadataOfClassFromAlias2.types
new file mode 100644
index 00000000000..20979a5c77d
--- /dev/null
+++ b/tests/baselines/reference/metadataOfClassFromAlias2.types
@@ -0,0 +1,30 @@
+=== tests/cases/compiler/auxiliry.ts ===
+export class SomeClass {
+>SomeClass : SomeClass
+
+    field: string;
+>field : string
+}
+
+=== tests/cases/compiler/test.ts ===
+import { SomeClass } from './auxiliry';
+>SomeClass : typeof SomeClass
+
+function annotation(): PropertyDecorator {
+>annotation : () => PropertyDecorator
+>PropertyDecorator : PropertyDecorator
+
+    return (target: any): void => { };
+>(target: any): void => { } : (target: any) => void
+>target : any
+}
+export class ClassA {
+>ClassA : ClassA
+
+    @annotation() array: SomeClass | null | string;
+>annotation() : PropertyDecorator
+>annotation : () => PropertyDecorator
+>array : string | SomeClass
+>SomeClass : SomeClass
+>null : null
+}
diff --git a/tests/baselines/reference/metadataOfUnionWithNull.js b/tests/baselines/reference/metadataOfUnionWithNull.js
index cc594ae326d..0c834be9687 100644
--- a/tests/baselines/reference/metadataOfUnionWithNull.js
+++ b/tests/baselines/reference/metadataOfUnionWithNull.js
@@ -65,15 +65,15 @@ var B = (function () {
 }());
 __decorate([
     PropDeco,
-    __metadata("design:type", String)
+    __metadata("design:type", Object)
 ], B.prototype, "x");
 __decorate([
     PropDeco,
-    __metadata("design:type", Boolean)
+    __metadata("design:type", Object)
 ], B.prototype, "y");
 __decorate([
     PropDeco,
-    __metadata("design:type", String)
+    __metadata("design:type", Object)
 ], B.prototype, "z");
 __decorate([
     PropDeco,
@@ -89,11 +89,11 @@ __decorate([
 ], B.prototype, "c");
 __decorate([
     PropDeco,
-    __metadata("design:type", void 0)
+    __metadata("design:type", Object)
 ], B.prototype, "d");
 __decorate([
     PropDeco,
-    __metadata("design:type", typeof Symbol === "function" ? Symbol : Object)
+    __metadata("design:type", Object)
 ], B.prototype, "e");
 __decorate([
     PropDeco,
@@ -101,13 +101,13 @@ __decorate([
 ], B.prototype, "f");
 __decorate([
     PropDeco,
-    __metadata("design:type", A)
+    __metadata("design:type", Object)
 ], B.prototype, "g");
 __decorate([
     PropDeco,
-    __metadata("design:type", B)
+    __metadata("design:type", Object)
 ], B.prototype, "h");
 __decorate([
     PropDeco,
-    __metadata("design:type", typeof Symbol === "function" ? Symbol : Object)
+    __metadata("design:type", Object)
 ], B.prototype, "j");
diff --git a/tests/cases/compiler/metadataOfClassFromAlias.ts b/tests/cases/compiler/metadataOfClassFromAlias.ts
new file mode 100644
index 00000000000..c7407c8d766
--- /dev/null
+++ b/tests/cases/compiler/metadataOfClassFromAlias.ts
@@ -0,0 +1,18 @@
+// @experimentalDecorators: true
+// @emitDecoratorMetadata: true
+// @target: es5
+// @module: commonjs
+
+// @filename: auxiliry.ts
+export class SomeClass {
+    field: string;
+}
+
+//@filename: test.ts
+import { SomeClass } from './auxiliry';
+function annotation(): PropertyDecorator {
+    return (target: any): void => { };
+}
+export class ClassA {
+    @annotation() array: SomeClass | null;
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/metadataOfClassFromAlias2.ts b/tests/cases/compiler/metadataOfClassFromAlias2.ts
new file mode 100644
index 00000000000..05c44d9c677
--- /dev/null
+++ b/tests/cases/compiler/metadataOfClassFromAlias2.ts
@@ -0,0 +1,18 @@
+// @experimentalDecorators: true
+// @emitDecoratorMetadata: true
+// @target: es5
+// @module: commonjs
+
+// @filename: auxiliry.ts
+export class SomeClass {
+    field: string;
+}
+
+//@filename: test.ts
+import { SomeClass } from './auxiliry';
+function annotation(): PropertyDecorator {
+    return (target: any): void => { };
+}
+export class ClassA {
+    @annotation() array: SomeClass | null | string;
+}
\ No newline at end of file