--- a/dom/media/AudioCompactor.h
+++ b/dom/media/AudioCompactor.h
@@ -44,17 +44,17 @@ public:
             uint32_t aFrames, uint32_t aChannels, CopyFunc aCopyFunc)
   {
     // If we are losing more than a reasonable amount to padding, try to chunk
     // the data.
     size_t maxSlop = AudioDataSize(aFrames, aChannels) / MAX_SLOP_DIVISOR;
 
     while (aFrames > 0) {
       uint32_t samples = GetChunkSamples(aFrames, aChannels, maxSlop);
-      if (aFrames * aChannels > mSamplesPadding) {
+      if (samples / aChannels > mSamplesPadding / aChannels + 1) {
         samples -= mSamplesPadding;
       }
       AlignedAudioBuffer buffer(samples);
       if (!buffer) {
         return false;
       }
 
       // Copy audio data to buffer using caller-provided functor.