diff --git a/dom/camera/CameraPreviewMediaStream.cpp b/dom/camera/CameraPreviewMediaStream.cpp
index b00492a3e055..d5ea13795eb3 100644
--- a/dom/camera/CameraPreviewMediaStream.cpp
+++ b/dom/camera/CameraPreviewMediaStream.cpp
@@ -127,6 +127,7 @@ CameraPreviewMediaStream::OnPreviewStateChange(bool aActive)
         l->NotifyQueuedTrackChanges(mFakeMediaStreamGraph, TRACK_VIDEO, 0,
                                     MediaStreamListener::TRACK_EVENT_CREATED,
                                     tmpSegment);
+        l->NotifyFinishedTrackCreation(mFakeMediaStreamGraph);
       }
     }
   }
diff --git a/dom/media/DOMMediaStream.cpp b/dom/media/DOMMediaStream.cpp
index 9d78ed62bdef..b331a06f161c 100644
--- a/dom/media/DOMMediaStream.cpp
+++ b/dom/media/DOMMediaStream.cpp
@@ -98,6 +98,35 @@ public:
     }
   }
 
+  class TracksCreatedRunnable : public nsRunnable {
+  public:
+    explicit TracksCreatedRunnable(StreamListener* aListener)
+      : mListener(aListener)
+    {
+    }
+
+    NS_IMETHOD Run()
+    {
+      MOZ_ASSERT(NS_IsMainThread());
+
+      DOMMediaStream* stream = mListener->GetStream();
+      if (!stream) {
+        return NS_OK;
+      }
+
+      stream->TracksCreated();
+      return NS_OK;
+    }
+
+    nsRefPtr<StreamListener> mListener;
+  };
+
+  virtual void NotifyFinishedTrackCreation(MediaStreamGraph* aGraph) MOZ_OVERRIDE
+  {
+    nsRefPtr<TracksCreatedRunnable> runnable = new TracksCreatedRunnable(this);
+    aGraph->DispatchToMainThreadAfterStreamStateUpdate(runnable.forget());
+  }
+
 private:
   // These fields may only be accessed on the main thread
   DOMMediaStream* mStream;
@@ -145,7 +174,7 @@ NS_INTERFACE_MAP_END_INHERITING(DOMMediaStream)
 
 DOMMediaStream::DOMMediaStream()
   : mLogicalStreamStartTime(0),
-    mStream(nullptr), mHintContents(0), mTrackTypesAvailable(0),
+    mStream(nullptr), mTracksCreated(false),
     mNotifiedOfMediaStreamGraphShutdown(false), mCORSMode(CORS_NONE)
 {
   nsresult rv;
@@ -475,10 +504,18 @@ DOMMediaStream::OnTracksAvailable(OnTracksAvailableCallback* aRunnable)
   CheckTracksAvailable();
 }
 
+void
+DOMMediaStream::TracksCreated()
+{
+  MOZ_ASSERT(!mTracks.IsEmpty());
+  mTracksCreated = true;
+  CheckTracksAvailable();
+}
+
 void
 DOMMediaStream::CheckTracksAvailable()
 {
-  if (mTrackTypesAvailable == 0) {
+  if (!mTracksCreated) {
     return;
   }
   nsTArray<nsAutoPtr<OnTracksAvailableCallback> > callbacks;
diff --git a/dom/media/DOMMediaStream.h b/dom/media/DOMMediaStream.h
index d48ea63e6a74..2c7aae9b2dae 100644
--- a/dom/media/DOMMediaStream.h
+++ b/dom/media/DOMMediaStream.h
@@ -279,6 +279,10 @@ protected:
   already_AddRefed<AudioTrack> CreateAudioTrack(AudioStreamTrack* aStreamTrack);
   already_AddRefed<VideoTrack> CreateVideoTrack(VideoStreamTrack* aStreamTrack);
 
+  // Called when MediaStreamGraph has finished an iteration where tracks were
+  // created.
+  void TracksCreated();
+
   void CheckTracksAvailable();
 
   class StreamListener;
@@ -299,6 +303,9 @@ protected:
 
   nsTArray<nsAutoPtr<OnTracksAvailableCallback> > mRunOnTracksAvailable;
 
+  // Set to true after MediaStreamGraph has created tracks for mStream.
+  bool mTracksCreated;
+
   nsString mID;
 
   // Keep these alive until the stream finishes
diff --git a/dom/media/MediaStreamGraph.cpp b/dom/media/MediaStreamGraph.cpp
index 94945177324b..c19e8fcaf404 100644
--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -190,11 +190,11 @@ MediaStreamGraphImpl::ExtractPendingInput(SourceMediaStream* aStream,
       }
     }
     finished = aStream->mUpdateFinished;
+    bool notifiedTrackCreated = false;
     for (int32_t i = aStream->mUpdateTracks.Length() - 1; i >= 0; --i) {
       SourceMediaStream::TrackData* data = &aStream->mUpdateTracks[i];
       aStream->ApplyTrackDisabling(data->mID, data->mData);
-      for (uint32_t j = 0; j < aStream->mListeners.Length(); ++j) {
-        MediaStreamListener* l = aStream->mListeners[j];
+      for (MediaStreamListener* l : aStream->mListeners) {
         StreamTime offset = (data->mCommands & SourceMediaStream::TRACK_CREATE)
             ? data->mStart : aStream->mBuffer.FindTrack(data->mID)->GetSegment()->GetDuration();
         l->NotifyQueuedTrackChanges(this, data->mID,
@@ -212,6 +212,7 @@ MediaStreamGraphImpl::ExtractPendingInput(SourceMediaStream* aStream,
         // data->mData with an empty clone.
         data->mData = segment->CreateEmptyClone();
         data->mCommands &= ~SourceMediaStream::TRACK_CREATE;
+        notifiedTrackCreated = true;
       } else if (data->mData->GetDuration() > 0) {
         MediaSegment* dest = aStream->mBuffer.FindTrack(data->mID)->GetSegment();
         STREAM_LOG(PR_LOG_DEBUG+1, ("SourceMediaStream %p track %d, advancing end from %lld to %lld",
@@ -226,6 +227,11 @@ MediaStreamGraphImpl::ExtractPendingInput(SourceMediaStream* aStream,
         aStream->mUpdateTracks.RemoveElementAt(i);
       }
     }
+    if (notifiedTrackCreated) {
+      for (MediaStreamListener* l : aStream->mListeners) {
+        l->NotifyFinishedTrackCreation(this);
+      }
+    }
     if (!aStream->mFinished) {
       aStream->mBuffer.AdvanceKnownTracksTime(aStream->mUpdateKnownTracksTime);
     }
@@ -1938,6 +1944,9 @@ MediaStream::EnsureTrack(TrackID aTrackId)
       l->NotifyQueuedTrackChanges(Graph(), aTrackId, 0,
                                   MediaStreamListener::TRACK_EVENT_CREATED,
                                   *segment);
+      // TODO If we ever need to ensure several tracks at once, we will have to
+      // change this.
+      l->NotifyFinishedTrackCreation(Graph());
     }
     track = &mBuffer.AddTrack(aTrackId, 0, segment.forget());
   }
diff --git a/dom/media/MediaStreamGraph.h b/dom/media/MediaStreamGraph.h
index 09f38808a082..522537e36a2f 100644
--- a/dom/media/MediaStreamGraph.h
+++ b/dom/media/MediaStreamGraph.h
@@ -177,6 +177,13 @@ public:
                                         StreamTime aTrackOffset,
                                         uint32_t aTrackEvents,
                                         const MediaSegment& aQueuedMedia) {}
+
+  /**
+   * Notify that all new tracks this iteration have been created.
+   * This is to ensure that tracks added atomically to MediaStreamGraph
+   * are also notified of atomically to MediaStreamListeners.
+   */
+  virtual void NotifyFinishedTrackCreation(MediaStreamGraph* aGraph) {}
 };
 
 /**
diff --git a/dom/media/TrackUnionStream.cpp b/dom/media/TrackUnionStream.cpp
index 5bb673fa2ca0..c7d545ec539b 100644
--- a/dom/media/TrackUnionStream.cpp
+++ b/dom/media/TrackUnionStream.cpp
@@ -94,6 +94,7 @@ TrackUnionStream::TrackUnionStream(DOMMediaStream* aWrapper) :
       if (!stream->HasCurrentData()) {
         allHaveCurrentData = false;
       }
+      bool trackAdded = false;
       for (StreamBuffer::TrackIter tracks(stream->GetStreamBuffer());
            !tracks.IsEnded(); tracks.Next()) {
         bool found = false;
@@ -115,12 +116,18 @@ TrackUnionStream::TrackUnionStream(DOMMediaStream* aWrapper) :
         }
         if (!found && (!mFilterCallback || mFilterCallback(tracks.get()))) {
           bool trackFinished = false;
+          trackAdded = true;
           uint32_t mapIndex = AddTrack(mInputs[i], tracks.get(), aFrom);
           CopyTrackData(tracks.get(), mapIndex, aFrom, aTo, &trackFinished);
           mappedTracksFinished.AppendElement(trackFinished);
           mappedTracksWithMatchingInputTracks.AppendElement(true);
         }
       }
+      if (trackAdded) {
+        for (MediaStreamListener* l : mListeners) {
+          l->NotifyFinishedTrackCreation(Graph());
+        }
+      }
     }
     for (int32_t i = mTrackMap.Length() - 1; i >= 0; --i) {
       if (mappedTracksFinished[i]) {