diff --git a/modules/angular2/src/facade/async.ts b/modules/angular2/src/facade/async.ts
index 7ee58ead00..e3602a6249 100644
--- a/modules/angular2/src/facade/async.ts
+++ b/modules/angular2/src/facade/async.ts
@@ -39,7 +39,7 @@ export class ObservableWrapper {
     return emitter.subscribe({next: onNext, error: onError, complete: onComplete});
   }
 
-  static isObservable(obs: any): boolean { return obs instanceof RxObservable; }
+  static isObservable(obs: any): boolean { return !!obs.subscribe; }
 
   /**
    * Returns whether `obs` has any subscribers listening to events.