diff --git a/spec/operators/expand-spec.js b/spec/operators/expand-spec.js
index f18d5292e8..5b605c2bbd 100644
--- a/spec/operators/expand-spec.js
+++ b/spec/operators/expand-spec.js
@@ -1,6 +1,7 @@
 /* globals describe, it, expect, expectObservable, hot, cold */
 var Rx = require('../../dist/cjs/Rx');
 var Observable = Rx.Observable;
+var Promise = require('promise');
 
 describe('Observable.prototype.expand()', function () {
   it('should map and recursively flatten', function() {
@@ -54,4 +55,65 @@ describe('Observable.prototype.expand()', function () {
       return Observable.of(x + x); // scalar
     })).toBe(expected, values);
   });
+  
+  it('should recursively flatten promises', function(done) {
+    var expected = [1, 2, 4, 8, 16];
+    Observable.of(1)
+      .expand(function(x) {
+        if(x === 16) {
+          return Observable.empty();
+        }
+        return Promise.resolve(x + x);
+      })
+      .subscribe(function(x) {
+        expect(x).toBe(expected.shift());
+      }, null, function(){
+        expect(expected.length).toBe(0);
+        done();
+      });
+  });
+  
+  it('should recursively flatten Arrays', function(done) {
+    var expected = [1, 2, 4, 8, 16];
+    Observable.of(1)
+      .expand(function(x) {
+        if(x === 16) {
+          return Observable.empty();
+        }
+        return [x + x];
+      })
+      .subscribe(function(x) {
+        expect(x).toBe(expected.shift());
+      }, null, function(){
+        expect(expected.length).toBe(0);
+        done();
+      });
+  });
+  
+  it('should recursively flatten lowercase-o observables', function(done) {
+    var expected = [1, 2, 4, 8, 16];
+    
+    Observable.of(1)
+      .expand(function(x) {
+        if(x === 16) {
+          return Observable.empty();
+        }
+        
+        var ish = {
+          subscribe: function(observer){
+            observer.next(x + x);
+            observer.complete();
+          }
+        };
+        
+        ish[Symbol.observable] = function(){ return this; };
+        return ish;
+      })
+      .subscribe(function(x) {
+        expect(x).toBe(expected.shift());
+      }, null, function(){
+        expect(expected.length).toBe(0);
+        done();
+      });
+  });
 });
\ No newline at end of file
diff --git a/spec/operators/switch-spec.js b/spec/operators/switch-spec.js
index 4e38163a3a..52599cd0f1 100644
--- a/spec/operators/switch-spec.js
+++ b/spec/operators/switch-spec.js
@@ -5,7 +5,7 @@ var Promise = require('promise');
 var Observable = Rx.Observable;
 var immediateScheduler = Rx.Scheduler.immediate;
 
-fdescribe('Observable.prototype.switch()', function(){
+describe('Observable.prototype.switch()', function(){
   it("should switch to each immediately-scheduled inner Observable", function (done) {
     var a = Observable.of(1, 2, 3, immediateScheduler);
     var b = Observable.of(4, 5, 6, immediateScheduler);
diff --git a/src/operators/expand-support.ts b/src/operators/expand-support.ts
index c93614e20e..c1db02648e 100644
--- a/src/operators/expand-support.ts
+++ b/src/operators/expand-support.ts
@@ -9,6 +9,8 @@ import ScalarObservable from '../observables/ScalarObservable';
 
 import tryCatch from '../util/tryCatch';
 import {errorObject} from '../util/errorObject';
+import OuterSubscriber from '../OuterSubscriber';
+import subscribeToResult from '../util/subscribeToResult';
 
 export class ExpandOperator<T, R> implements Operator<T, R> {
   constructor(private project: (value: T, index: number) => Observable<any>, 
@@ -20,11 +22,11 @@ export class ExpandOperator<T, R> implements Operator<T, R> {
   }
 }
 
-export class ExpandSubscriber<T, R> extends Subscriber<T> {
+export class ExpandSubscriber<T, R> extends OuterSubscriber<T, R> {
   private index: number = 0;
   private active: number = 0;
   private hasCompleted: boolean = false;
-  private buffer: T[];
+  private buffer: any[];
   
   constructor(destination: Observer<T>, private project: (value: T, index: number) => Observable<R>, 
     private concurrent: number = Number.POSITIVE_INFINITY) {
@@ -34,7 +36,7 @@ export class ExpandSubscriber<T, R> extends Subscriber<T> {
     }
   }
   
-  _next(value: T) {
+  _next(value: any) {
     const index = this.index++;
     this.destination.next(value);
     if(this.active < this.concurrent) {
@@ -46,7 +48,7 @@ export class ExpandSubscriber<T, R> extends Subscriber<T> {
           this._next(result.value);
         } else {
           this.active++;
-          this.add(result.subscribe(new ExpandInnerSubscriber(this.destination, this)));
+          this.add(subscribeToResult<T, R>(this, result, value, index));
         }
       }
     } else {
@@ -72,18 +74,8 @@ export class ExpandSubscriber<T, R> extends Subscriber<T> {
       this.destination.complete();
     }
   }
-}
-
-export class ExpandInnerSubscriber<T, R> extends Subscriber<T> {
-  constructor(destination: Observer<T>, private parent: ExpandSubscriber<T, R>) {
-    super(destination);
-  }
   
-  _next(value) {
-    this.parent._next(value);
-  }
-  
-  _complete() {
-    this.parent.notifyComplete(this);
+  notifyNext(innerValue: R, outerValue: T, innerIndex: number, outerIndex: number) {
+    this._next(innerValue);
   }
 }
diff --git a/src/operators/mergeMap-support.ts b/src/operators/mergeMap-support.ts
index 785342c88a..f8eac64fa1 100644
--- a/src/operators/mergeMap-support.ts
+++ b/src/operators/mergeMap-support.ts
@@ -51,7 +51,7 @@ export class MergeMapSubscriber<T, R, R2> extends OuterSubscriber<T, R> {
   }
   
   _innerSub(ish: any, value: T, index: number) {
-    this.add(subscribeToResult<T,R,R2>(this, ish, value, index));
+    this.add(subscribeToResult<T, R>(this, ish, value, index));
   }
   
   _complete() {
diff --git a/src/operators/mergeMapTo-support.ts b/src/operators/mergeMapTo-support.ts
index d9846387c0..9a03c339c1 100644
--- a/src/operators/mergeMapTo-support.ts
+++ b/src/operators/mergeMapTo-support.ts
@@ -51,7 +51,7 @@ export class MergeMapToSubscriber<T, R, R2> extends OuterSubscriber<T, R> {
   }
   
   _innerSub(ish: any, destination: Observer<R>, resultSelector: (innerValue: R, outerValue: T, innerIndex: number, outerIndex: number) => R2, value: T, index: number) {
-    this.add(subscribeToResult<T,R,R2>(this, ish, value, index));
+    this.add(subscribeToResult<T, R>(this, ish, value, index));
   }
   
   _complete() {
diff --git a/src/util/subscribeToResult.ts b/src/util/subscribeToResult.ts
index 9ed906101a..97a057cb40 100644
--- a/src/util/subscribeToResult.ts
+++ b/src/util/subscribeToResult.ts
@@ -11,7 +11,7 @@ import OuterSubscriber from '../OuterSubscriber';
 
 const isArray = Array.isArray;
 
-export default function subscribeToResult<T, R, R2>(outerSubscriber: OuterSubscriber<T, R>, 
+export default function subscribeToResult<T, R>(outerSubscriber: OuterSubscriber<T, R>, 
   result: any, outerValue?: T, outerIndex?: number): Subscription<T> {
     let destination: Subscriber<R> = new InnerSubscriber(outerSubscriber, outerValue, outerIndex);