diff --git a/ember/ember.d.ts b/ember/ember.d.ts
index a35d51eb9..48aa81aa2 100644
--- a/ember/ember.d.ts
+++ b/ember/ember.d.ts
@@ -58,7 +58,7 @@ declare module EmberStates {
           @arg {String} label optional string for labeling the promise. Useful for tooling.
           @return {Promise}
          */
-        then(onFulfilled: Function, onRejected: Function, label?: string): Ember.RSVP.Promise;
+        then(onFulfilled: Function, onRejected?: Function, label?: string): Ember.RSVP.Promise;
 
         /**
           Forwards to the internal `promise` property which you can