diff --git a/dom/media/mediasource/MediaSourceDemuxer.cpp b/dom/media/mediasource/MediaSourceDemuxer.cpp
index 73950e1a87..616693720a 100644
--- a/dom/media/mediasource/MediaSourceDemuxer.cpp
+++ b/dom/media/mediasource/MediaSourceDemuxer.cpp
@@ -465,10 +465,12 @@ MediaSourceTrackDemuxer::DoGetSamples(int32_t aNumSamples)
   }
   RefPtr<SamplesHolder> samples = new SamplesHolder;
   samples->mSamples.AppendElement(sample);
-  if (mNextRandomAccessPoint.ToMicroseconds() <= sample->mTime) {
+  {
     MonitorAutoLock mon(mMonitor);
-    mNextRandomAccessPoint =
-      mManager->GetNextRandomAccessPoint(mType, MediaSourceDemuxer::EOS_FUZZ);
+    if (mNextRandomAccessPoint.ToMicroseconds() <= sample->mTime) {
+      mNextRandomAccessPoint =
+        mManager->GetNextRandomAccessPoint(mType, MediaSourceDemuxer::EOS_FUZZ);
+    }
   }
   return SamplesPromise::CreateAndResolve(samples, __func__);
 }