--- a/dom/media/MediaCache.cpp
+++ b/dom/media/MediaCache.cpp
@@ -2400,28 +2400,28 @@ MediaCacheStream::CloseInternal(AutoLock
 
   // Queue an Update since we may have created more free space.
   mMediaCache->QueueUpdate(aLock);
 }
 
 void
 MediaCacheStream::Pin()
 {
-  // TODO: Assert non-main thread.
+  MOZ_ASSERT(!NS_IsMainThread());
   AutoLock lock(mMediaCache->Monitor());
   ++mPinCount;
   // Queue an Update since we may no longer want to read more into the
   // cache, if this stream's block have become non-evictable
   mMediaCache->QueueUpdate(lock);
 }
 
 void
 MediaCacheStream::Unpin()
 {
-  // TODO: Assert non-main thread.
+  MOZ_ASSERT(!NS_IsMainThread());
   AutoLock lock(mMediaCache->Monitor());
   NS_ASSERTION(mPinCount > 0, "Unbalanced Unpin");
   --mPinCount;
   // Queue an Update since we may be able to read more into the
   // cache, if this stream's block have become evictable
   mMediaCache->QueueUpdate(lock);
 }