--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -973,19 +973,19 @@ void MediaDecoderStateMachine::MaybeStar
 
   DispatchDecodeTasksIfNeeded();
 }
 
 void
 MediaDecoderStateMachine::MaybeStartBuffering()
 {
   MOZ_ASSERT(OnTaskQueue());
-
-  if (mState == DECODER_STATE_DECODING &&
-      mPlayState == MediaDecoder::PLAY_STATE_PLAYING &&
+  MOZ_ASSERT(mState == DECODER_STATE_DECODING);
+
+  if (mPlayState == MediaDecoder::PLAY_STATE_PLAYING &&
       mResource->IsExpectingMoreData()) {
     bool shouldBuffer;
     if (mReader->UseBufferingHeuristics()) {
       shouldBuffer = HasLowDecodedData(EXHAUSTED_DATA_MARGIN_USECS) &&
                      (JustExitedQuickBuffering() || HasLowUndecodedData());
     } else {
       MOZ_ASSERT(mReader->IsWaitForDataSupported());
       shouldBuffer = (OutOfDecodedAudio() && mReader->IsWaitingAudioData()) ||