--- a/dom/media/mediasource/TrackBuffer.cpp
+++ b/dom/media/mediasource/TrackBuffer.cpp
@@ -480,16 +480,21 @@ TrackBuffer::QueueInitializeDecoder(Sour
     return false;
   }
   return true;
 }
 
 void
 TrackBuffer::InitializeDecoder(SourceBufferDecoder* aDecoder)
 {
+  if (!mParentDecoder) {
+    MSE_DEBUG("TrackBuffer(%p) was shutdown. Aborting initialization.",
+              this);
+    return;
+  }
   // ReadMetadata may block the thread waiting on data, so we must be able
   // to leave the monitor while we call it. For the rest of this function
   // we want to hold the monitor though, since we run on a different task queue
   // from the reader and interact heavily with it.
   mParentDecoder->GetReentrantMonitor().AssertNotCurrentThreadIn();
   ReentrantMonitorAutoEnter mon(mParentDecoder->GetReentrantMonitor());
 
   if (mCurrentDecoder != aDecoder) {
@@ -582,16 +587,21 @@ TrackBuffer::InitializeDecoder(SourceBuf
     mInitializationPromise.RejectIfExists(NS_ERROR_FAILURE, __func__);
     return;
   }
 }
 
 void
 TrackBuffer::CompleteInitializeDecoder(SourceBufferDecoder* aDecoder)
 {
+  if (!mParentDecoder) {
+    MSE_DEBUG("TrackBuffer(%p) was shutdown. Aborting initialization.",
+              this);
+    return;
+  }
   ReentrantMonitorAutoEnter mon(mParentDecoder->GetReentrantMonitor());
   if (mCurrentDecoder != aDecoder) {
     MSE_DEBUG("TrackBuffer(%p) append was cancelled. Aborting initialization.",
               this);
     // If we reached this point, the SourceBuffer would have disconnected
     // the promise. So no need to reject it.
     return;
   }