diff --git a/src/Observable.ts b/src/Observable.ts
index 5e713889229..81c6b60f682 100644
--- a/src/Observable.ts
+++ b/src/Observable.ts
@@ -10,7 +10,9 @@ import {IfObservable} from './observable/IfObservable';
 import {ErrorObservable} from './observable/ErrorObservable';
 
 export interface Subscribable<T> {
-  subscribe(observer: Observer<T>): AnonymousSubscription;
+  subscribe(observerOrNext?: PartialObserver<T> | ((value: T) => void),
+            error?: (error: any) => void,
+            complete?: () => void): AnonymousSubscription;
 }
 
 export type SubscribableOrPromise<T> = Subscribable<T> | Promise<T>;
diff --git a/src/operator/concatAll.ts b/src/operator/concatAll.ts
index 5ff3c957573..c579a4c9b3d 100644
--- a/src/operator/concatAll.ts
+++ b/src/operator/concatAll.ts
@@ -1,3 +1,4 @@
+import {Subscribable} from '../Observable';
 import {MergeAllOperator} from './mergeAll';
 
 /**
@@ -48,4 +49,5 @@ export function concatAll<T>(): T {
 
 export interface ConcatAllSignature<T> {
   (): T;
+  <R>(): Subscribable<R>;
 }