diff --git a/greensock/greensock.d.ts b/greensock/greensock.d.ts
index 4cf521e156..42fa6aa853 100644
--- a/greensock/greensock.d.ts
+++ b/greensock/greensock.d.ts
@@ -7,7 +7,7 @@
 // Version 1.1 (TypeScript 0.9)
 
 interface IDispatcher {
-    addEventListener(type:string, callback:Function, scope:Object, useParam:boolean, priority:number):void;
+    addEventListener(type:string, callback:Function, scope?:Object, useParam?:boolean, priority?:number):void;
     removeEventListener(type:string, callback:Function):void;
 }