diff --git a/src/compiler/factory.ts b/src/compiler/factory.ts
index 2b41f13f8a..943d011c35 100644
--- a/src/compiler/factory.ts
+++ b/src/compiler/factory.ts
@@ -303,7 +303,7 @@ namespace ts {
             : node;
     }
 
-    export function createProperty(decorators: Decorator[] | undefined, modifiers: Modifier[] | undefined, name: string | PropertyName, questionToken: QuestionToken | undefined, type: TypeNode | undefined, initializer: Expression) {
+    export function createProperty(decorators: Decorator[] | undefined, modifiers: Modifier[] | undefined, name: string | PropertyName, questionToken: QuestionToken | undefined, type: TypeNode | undefined, initializer: Expression | undefined) {
         const node = <PropertyDeclaration>createSynthesizedNode(SyntaxKind.PropertyDeclaration);
         node.decorators = asNodeArray(decorators);
         node.modifiers = asNodeArray(modifiers);
@@ -314,7 +314,7 @@ namespace ts {
         return node;
     }
 
-    export function updateProperty(node: PropertyDeclaration, decorators: Decorator[] | undefined, modifiers: Modifier[] | undefined, name: PropertyName, type: TypeNode | undefined, initializer: Expression) {
+    export function updateProperty(node: PropertyDeclaration, decorators: Decorator[] | undefined, modifiers: Modifier[] | undefined, name: PropertyName, type: TypeNode | undefined, initializer: Expression | undefined) {
         return node.decorators !== decorators
             || node.modifiers !== modifiers
             || node.name !== name