--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -909,23 +909,39 @@ MediaStreamGraphImpl::MarkStreamBlocking
 }
 
 void
 MediaStreamGraphImpl::RecomputeBlockingAt(const nsTArray<MediaStream*>& aStreams,
                                           GraphTime aTime,
                                           GraphTime aEndBlockingDecisions,
                                           GraphTime* aEnd)
 {
+  class MOZ_STACK_CLASS AfterLoop
+  {
+  public:
+    AfterLoop(MediaStream* aStream, GraphTime& aTime)
+      : mStream(aStream)
+      , mTime(aTime)
+    {}
+
+    ~AfterLoop()
+    {
+      mStream->mBlocked.SetAtAndAfter(mTime, mStream->mBlockInThisPhase);
+    }
+
+  private:
+    MediaStream* mStream;
+    GraphTime& mTime;
+  };
+
   for (uint32_t i = 0; i < aStreams.Length(); ++i) {
     MediaStream* stream = aStreams[i];
     stream->mBlockInThisPhase = false;
-  }
-
-  for (uint32_t i = 0; i < aStreams.Length(); ++i) {
-    MediaStream* stream = aStreams[i];
+
+    AfterLoop al(stream, aTime);
 
     if (stream->mFinished) {
       GraphTime endTime = StreamTimeToGraphTime(stream,
          stream->GetStreamBuffer().GetAllTracksEnd());
       if (endTime <= aTime) {
         STREAM_LOG(PR_LOG_DEBUG+1, ("MediaStream %p is blocked due to being finished", stream));
         // We'll block indefinitely
         MarkStreamBlocking(stream);
@@ -951,22 +967,18 @@ MediaStreamGraphImpl::RecomputeBlockingA
     bool underrun = WillUnderrun(stream, aTime, aEndBlockingDecisions, aEnd);
     if (underrun) {
       // We'll block indefinitely
       MarkStreamBlocking(stream);
       *aEnd = std::min(*aEnd, aEndBlockingDecisions);
       continue;
     }
   }
+
   NS_ASSERTION(*aEnd > aTime, "Failed to advance!");
-
-  for (uint32_t i = 0; i < aStreams.Length(); ++i) {
-    MediaStream* stream = aStreams[i];
-    stream->mBlocked.SetAtAndAfter(aTime, stream->mBlockInThisPhase);
-  }
 }
 
 void
 MediaStreamGraphImpl::NotifyHasCurrentData(MediaStream* aStream)
 {
   if (!aStream->mNotifiedHasCurrentData && aStream->mHasCurrentData) {
     for (uint32_t j = 0; j < aStream->mListeners.Length(); ++j) {
       MediaStreamListener* l = aStream->mListeners[j];