diff --git a/dom/media/MediaStreamGraph.cpp b/dom/media/MediaStreamGraph.cpp
index ccafd9506602..6e51d5d52736 100644
--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -914,13 +914,29 @@ MediaStreamGraphImpl::RecomputeBlockingAt(const nsTArray<MediaStream*>& aStreams
                                           GraphTime aEndBlockingDecisions,
                                           GraphTime* aEnd)
 {
-  for (uint32_t i = 0; i < aStreams.Length(); ++i) {
-    MediaStream* stream = aStreams[i];
-    stream->mBlockInThisPhase = false;
-  }
+  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;
+
+    AfterLoop al(stream, aTime);
 
     if (stream->mFinished) {
       GraphTime endTime = StreamTimeToGraphTime(stream,
@@ -956,12 +972,8 @@ MediaStreamGraphImpl::RecomputeBlockingAt(const nsTArray<MediaStream*>& aStreams
       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);
-  }
+  NS_ASSERTION(*aEnd > aTime, "Failed to advance!");
 }
 
 void