diff --git a/content/media/AudioStream.cpp b/content/media/AudioStream.cpp
index c3c24b5b4c0..39b60a2b895 100644
--- a/content/media/AudioStream.cpp
+++ b/content/media/AudioStream.cpp
@@ -604,6 +604,10 @@ class BufferedAudioStream : public AudioStream
   int64_t GetPositionInFramesInternal();
   bool IsPaused();
   int32_t GetMinWriteSize();
+  // This method acquires the monitor and forward the call to the base
+  // class, to prevent a race on |mTimeStretcher|, in
+  // |AudioStream::EnsureTimeStretcherInitialized|.
+  void EnsureTimeStretcherInitialized();
 
 private:
   static long DataCallback_S(cubeb_stream*, void* aThis, void* aBuffer, long aFrames)
@@ -702,6 +706,13 @@ BufferedAudioStream::~BufferedAudioStream()
   Shutdown();
 }
 
+void
+BufferedAudioStream::EnsureTimeStretcherInitialized()
+{
+  MonitorAutoLock mon(mMonitor);
+  AudioStream::EnsureTimeStretcherInitialized();
+}
+
 nsresult
 BufferedAudioStream::Init(int32_t aNumChannels, int32_t aRate,
                             const dom::AudioChannelType aAudioChannelType)
@@ -962,7 +973,8 @@ BufferedAudioStream::GetTimeStretched(void* aBuffer, long aFrames)
 {
   long processedFrames = 0;
 
-  EnsureTimeStretcherInitialized();
+  // We need to call the non-locking version, because we already have the lock.
+  AudioStream::EnsureTimeStretcherInitialized();
 
   uint8_t* wpos = reinterpret_cast<uint8_t*>(aBuffer);
   double playbackRate = static_cast<double>(mInRate) / mOutRate;
diff --git a/content/media/AudioStream.h b/content/media/AudioStream.h
index 03ee4a8191e..ae73be00117 100644
--- a/content/media/AudioStream.h
+++ b/content/media/AudioStream.h
@@ -160,7 +160,7 @@ public:
   int GetChannels() { return mChannels; }
 
   // This should be called before attempting to use the time stretcher.
-  void EnsureTimeStretcherInitialized();
+  virtual void EnsureTimeStretcherInitialized();
   // Set playback rate as a multiple of the intrinsic playback rate. This is to
   // be called only with aPlaybackRate > 0.0.
   virtual nsresult SetPlaybackRate(double aPlaybackRate);