diff --git a/src/compiler/transformers/ts.ts b/src/compiler/transformers/ts.ts
index 877131b369c87..f791025807a25 100644
--- a/src/compiler/transformers/ts.ts
+++ b/src/compiler/transformers/ts.ts
@@ -1555,12 +1555,15 @@ namespace ts {
             return false;
         }
 
+        type SerializedEntityNameAsExpression = Identifier | BinaryExpression | PropertyAccessExpression;
+        type SerializedTypeNode = SerializedEntityNameAsExpression | VoidExpression | ConditionalExpression;
+
         /**
          * Serializes the type of a node for use with decorator type metadata.
          *
          * @param node The node that should have its type serialized.
          */
-        function serializeTypeOfNode(node: Node): Expression {
+        function serializeTypeOfNode(node: Node): SerializedTypeNode {
             switch (node.kind) {
                 case SyntaxKind.PropertyDeclaration:
                 case SyntaxKind.Parameter:
@@ -1582,7 +1585,7 @@ namespace ts {
          *
          * @param node The node that should have its parameter types serialized.
          */
-        function serializeParameterTypesOfNode(node: Node, container: ClassLikeDeclaration): Expression {
+        function serializeParameterTypesOfNode(node: Node, container: ClassLikeDeclaration): ArrayLiteralExpression {
             const valueDeclaration =
                 isClassLike(node)
                     ? getFirstConstructorWithBody(node)
@@ -1590,7 +1593,7 @@ namespace ts {
                         ? node
                         : undefined;
 
-            const expressions: Expression[] = [];
+            const expressions: SerializedTypeNode[] = [];
             if (valueDeclaration) {
                 const parameters = getParametersOfDecoratedDeclaration(valueDeclaration, container);
                 const numParameters = parameters.length;
@@ -1626,7 +1629,7 @@ namespace ts {
          *
          * @param node The node that should have its return type serialized.
          */
-        function serializeReturnTypeOfNode(node: Node): Expression {
+        function serializeReturnTypeOfNode(node: Node): SerializedTypeNode {
             if (isFunctionLike(node) && node.type) {
                 return serializeTypeNode(node.type);
             }
@@ -1655,13 +1658,16 @@ namespace ts {
          *
          * @param node The type node to serialize.
          */
-        function serializeTypeNode(node: TypeNode): Expression {
+        function serializeTypeNode(node: TypeNode): SerializedTypeNode {
             if (node === undefined) {
                 return createIdentifier("Object");
             }
 
             switch (node.kind) {
                 case SyntaxKind.VoidKeyword:
+                case SyntaxKind.UndefinedKeyword:
+                case SyntaxKind.NullKeyword:
+                case SyntaxKind.NeverKeyword:
                     return createVoidZero();
 
                 case SyntaxKind.ParenthesizedType:
@@ -1713,37 +1719,8 @@ namespace ts {
 
                 case SyntaxKind.IntersectionType:
                 case SyntaxKind.UnionType:
-                    {
-                        const unionOrIntersection = <UnionOrIntersectionTypeNode>node;
-                        let serializedUnion: Identifier;
-                        for (const typeNode of unionOrIntersection.types) {
-                            const serializedIndividual = serializeTypeNode(typeNode) as Identifier;
-                            // Non identifier
-                            if (serializedIndividual.kind !== SyntaxKind.Identifier) {
-                                serializedUnion = undefined;
-                                break;
-                            }
-
-                            // One of the individual is global object, return immediately
-                            if (serializedIndividual.text === "Object") {
-                                return serializedIndividual;
-                            }
-
-                            // Different types
-                            if (serializedUnion && serializedUnion.text !== serializedIndividual.text) {
-                                serializedUnion = undefined;
-                                break;
-                            }
-
-                            serializedUnion = serializedIndividual;
-                        }
+                    return serializeUnionOrIntersectionType(<UnionOrIntersectionTypeNode>node);
 
-                        // If we were able to find common type
-                        if (serializedUnion) {
-                            return serializedUnion;
-                        }
-                    }
-                    // Fallthrough
                 case SyntaxKind.TypeQuery:
                 case SyntaxKind.TypeOperator:
                 case SyntaxKind.IndexedAccessType:
@@ -1761,13 +1738,48 @@ namespace ts {
             return createIdentifier("Object");
         }
 
+        function serializeUnionOrIntersectionType(node: UnionOrIntersectionTypeNode): SerializedTypeNode {
+            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") {
+                    // 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)) {
+                    // Different types
+                    if (!isIdentifier(serializedUnion) ||
+                        !isIdentifier(serializedIndividual) ||
+                        serializedUnion.text !== serializedIndividual.text) {
+                        return createIdentifier("Object");
+                    }
+                }
+                else {
+                    // Initialize the union type
+                    serializedUnion = serializedIndividual;
+                }
+            }
+
+            // If we were able to find common type, use it
+            return serializedUnion;
+        }
+
         /**
          * Serializes a TypeReferenceNode to an appropriate JS constructor value for use with
          * decorator type metadata.
          *
          * @param node The type reference node.
          */
-        function serializeTypeReferenceNode(node: TypeReferenceNode) {
+        function serializeTypeReferenceNode(node: TypeReferenceNode): SerializedTypeNode {
             switch (resolver.getTypeReferenceSerializationKind(node.typeName, currentScope)) {
                 case TypeReferenceSerializationKind.Unknown:
                     const serialized = serializeEntityNameAsExpression(node.typeName, /*useFallback*/ true);
@@ -1822,7 +1834,7 @@ namespace ts {
          * @param useFallback A value indicating whether to use logical operators to test for the
          *                    entity name at runtime.
          */
-        function serializeEntityNameAsExpression(node: EntityName, useFallback: boolean): Expression {
+        function serializeEntityNameAsExpression(node: EntityName, useFallback: boolean): SerializedEntityNameAsExpression {
             switch (node.kind) {
                 case SyntaxKind.Identifier:
                     // Create a clone of the name with a new parent, and treat it as if it were
@@ -1855,8 +1867,8 @@ namespace ts {
          * @param useFallback A value indicating whether to use logical operators to test for the
          *                    qualified name at runtime.
          */
-        function serializeQualifiedNameAsExpression(node: QualifiedName, useFallback: boolean): Expression {
-            let left: Expression;
+        function serializeQualifiedNameAsExpression(node: QualifiedName, useFallback: boolean): PropertyAccessExpression {
+            let left: SerializedEntityNameAsExpression;
             if (node.left.kind === SyntaxKind.Identifier) {
                 left = serializeEntityNameAsExpression(node.left, useFallback);
             }
@@ -1881,7 +1893,7 @@ namespace ts {
          * Gets an expression that points to the global "Symbol" constructor at runtime if it is
          * available.
          */
-        function getGlobalSymbolNameWithFallback(): Expression {
+        function getGlobalSymbolNameWithFallback(): ConditionalExpression {
             return createConditional(
                 createTypeCheck(createIdentifier("Symbol"), "function"),
                 createIdentifier("Symbol"),
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 309236e01c1ad..c542fdb74f8bc 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -3591,6 +3591,10 @@ 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/metadataOfUnionWithNull.js b/tests/baselines/reference/metadataOfUnionWithNull.js
new file mode 100644
index 0000000000000..cc594ae326dc3
--- /dev/null
+++ b/tests/baselines/reference/metadataOfUnionWithNull.js
@@ -0,0 +1,113 @@
+//// [metadataOfUnionWithNull.ts]
+function PropDeco(target: Object, propKey: string | symbol) { }
+
+class A {
+}
+
+class B {
+    @PropDeco
+    x: "foo" | null;
+
+    @PropDeco
+    y: true | never;
+
+    @PropDeco
+    z: "foo" | undefined;
+
+    @PropDeco
+    a: null;
+
+    @PropDeco
+    b: never;
+
+    @PropDeco
+    c: undefined;
+
+    @PropDeco
+    d: undefined | null;
+
+    @PropDeco
+    e: symbol | null;
+
+    @PropDeco
+    f: symbol | A;
+
+    @PropDeco
+    g: A | null;
+
+    @PropDeco
+    h: null | B;
+
+    @PropDeco
+    j: null | symbol;
+}
+
+//// [metadataOfUnionWithNull.js]
+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);
+};
+function PropDeco(target, propKey) { }
+var A = (function () {
+    function A() {
+    }
+    return A;
+}());
+var B = (function () {
+    function B() {
+    }
+    return B;
+}());
+__decorate([
+    PropDeco,
+    __metadata("design:type", String)
+], B.prototype, "x");
+__decorate([
+    PropDeco,
+    __metadata("design:type", Boolean)
+], B.prototype, "y");
+__decorate([
+    PropDeco,
+    __metadata("design:type", String)
+], B.prototype, "z");
+__decorate([
+    PropDeco,
+    __metadata("design:type", void 0)
+], B.prototype, "a");
+__decorate([
+    PropDeco,
+    __metadata("design:type", void 0)
+], B.prototype, "b");
+__decorate([
+    PropDeco,
+    __metadata("design:type", void 0)
+], B.prototype, "c");
+__decorate([
+    PropDeco,
+    __metadata("design:type", void 0)
+], B.prototype, "d");
+__decorate([
+    PropDeco,
+    __metadata("design:type", typeof Symbol === "function" ? Symbol : Object)
+], B.prototype, "e");
+__decorate([
+    PropDeco,
+    __metadata("design:type", Object)
+], B.prototype, "f");
+__decorate([
+    PropDeco,
+    __metadata("design:type", A)
+], B.prototype, "g");
+__decorate([
+    PropDeco,
+    __metadata("design:type", B)
+], B.prototype, "h");
+__decorate([
+    PropDeco,
+    __metadata("design:type", typeof Symbol === "function" ? Symbol : Object)
+], B.prototype, "j");
diff --git a/tests/baselines/reference/metadataOfUnionWithNull.symbols b/tests/baselines/reference/metadataOfUnionWithNull.symbols
new file mode 100644
index 0000000000000..13316bc7cf19e
--- /dev/null
+++ b/tests/baselines/reference/metadataOfUnionWithNull.symbols
@@ -0,0 +1,89 @@
+=== tests/cases/compiler/metadataOfUnionWithNull.ts ===
+function PropDeco(target: Object, propKey: string | symbol) { }
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+>target : Symbol(target, Decl(metadataOfUnionWithNull.ts, 0, 18))
+>Object : Symbol(Object, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>propKey : Symbol(propKey, Decl(metadataOfUnionWithNull.ts, 0, 33))
+
+class A {
+>A : Symbol(A, Decl(metadataOfUnionWithNull.ts, 0, 63))
+}
+
+class B {
+>B : Symbol(B, Decl(metadataOfUnionWithNull.ts, 3, 1))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    x: "foo" | null;
+>x : Symbol(B.x, Decl(metadataOfUnionWithNull.ts, 5, 9))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    y: true | never;
+>y : Symbol(B.y, Decl(metadataOfUnionWithNull.ts, 7, 20))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    z: "foo" | undefined;
+>z : Symbol(B.z, Decl(metadataOfUnionWithNull.ts, 10, 20))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    a: null;
+>a : Symbol(B.a, Decl(metadataOfUnionWithNull.ts, 13, 25))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    b: never;
+>b : Symbol(B.b, Decl(metadataOfUnionWithNull.ts, 16, 12))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    c: undefined;
+>c : Symbol(B.c, Decl(metadataOfUnionWithNull.ts, 19, 13))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    d: undefined | null;
+>d : Symbol(B.d, Decl(metadataOfUnionWithNull.ts, 22, 17))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    e: symbol | null;
+>e : Symbol(B.e, Decl(metadataOfUnionWithNull.ts, 25, 24))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    f: symbol | A;
+>f : Symbol(B.f, Decl(metadataOfUnionWithNull.ts, 28, 21))
+>A : Symbol(A, Decl(metadataOfUnionWithNull.ts, 0, 63))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    g: A | null;
+>g : Symbol(B.g, Decl(metadataOfUnionWithNull.ts, 31, 18))
+>A : Symbol(A, Decl(metadataOfUnionWithNull.ts, 0, 63))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    h: null | B;
+>h : Symbol(B.h, Decl(metadataOfUnionWithNull.ts, 34, 16))
+>B : Symbol(B, Decl(metadataOfUnionWithNull.ts, 3, 1))
+
+    @PropDeco
+>PropDeco : Symbol(PropDeco, Decl(metadataOfUnionWithNull.ts, 0, 0))
+
+    j: null | symbol;
+>j : Symbol(B.j, Decl(metadataOfUnionWithNull.ts, 37, 16))
+}
diff --git a/tests/baselines/reference/metadataOfUnionWithNull.types b/tests/baselines/reference/metadataOfUnionWithNull.types
new file mode 100644
index 0000000000000..04a5b162d4c52
--- /dev/null
+++ b/tests/baselines/reference/metadataOfUnionWithNull.types
@@ -0,0 +1,97 @@
+=== tests/cases/compiler/metadataOfUnionWithNull.ts ===
+function PropDeco(target: Object, propKey: string | symbol) { }
+>PropDeco : (target: Object, propKey: string | symbol) => void
+>target : Object
+>Object : Object
+>propKey : string | symbol
+
+class A {
+>A : A
+}
+
+class B {
+>B : B
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    x: "foo" | null;
+>x : "foo"
+>null : null
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    y: true | never;
+>y : true
+>true : true
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    z: "foo" | undefined;
+>z : "foo"
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    a: null;
+>a : null
+>null : null
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    b: never;
+>b : never
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    c: undefined;
+>c : undefined
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    d: undefined | null;
+>d : null
+>null : null
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    e: symbol | null;
+>e : symbol
+>null : null
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    f: symbol | A;
+>f : symbol | A
+>A : A
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    g: A | null;
+>g : A
+>A : A
+>null : null
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    h: null | B;
+>h : B
+>null : null
+>B : B
+
+    @PropDeco
+>PropDeco : (target: Object, propKey: string | symbol) => void
+
+    j: null | symbol;
+>j : symbol
+>null : null
+}
diff --git a/tests/cases/compiler/metadataOfUnionWithNull.ts b/tests/cases/compiler/metadataOfUnionWithNull.ts
new file mode 100644
index 0000000000000..bb4d93189fc66
--- /dev/null
+++ b/tests/cases/compiler/metadataOfUnionWithNull.ts
@@ -0,0 +1,44 @@
+// @experimentalDecorators: true
+// @emitDecoratorMetadata: true
+function PropDeco(target: Object, propKey: string | symbol) { }
+
+class A {
+}
+
+class B {
+    @PropDeco
+    x: "foo" | null;
+
+    @PropDeco
+    y: true | never;
+
+    @PropDeco
+    z: "foo" | undefined;
+
+    @PropDeco
+    a: null;
+
+    @PropDeco
+    b: never;
+
+    @PropDeco
+    c: undefined;
+
+    @PropDeco
+    d: undefined | null;
+
+    @PropDeco
+    e: symbol | null;
+
+    @PropDeco
+    f: symbol | A;
+
+    @PropDeco
+    g: A | null;
+
+    @PropDeco
+    h: null | B;
+
+    @PropDeco
+    j: null | symbol;
+}
\ No newline at end of file