--- a/dom/media/MediaCache.cpp
+++ b/dom/media/MediaCache.cpp
@@ -2556,27 +2556,23 @@ MediaCacheStream::Init(int64_t aContentL
   mMediaCache = MediaCache::GetMediaCache(aContentLength);
   if (!mMediaCache) {
     return NS_ERROR_FAILURE;
   }
   mMediaCache->OpenStream(this);
   return NS_OK;
 }
 
-nsresult
+void
 MediaCacheStream::InitAsClone(MediaCacheStream* aOriginal)
 {
-  if (!aOriginal->IsAvailableForSharing())
-    return NS_ERROR_FAILURE;
+  MOZ_ASSERT(aOriginal->IsAvailableForSharing());
+  MOZ_ASSERT(!mMediaCache, "Has been initialized.");
+  MOZ_ASSERT(aOriginal->mMediaCache, "Don't clone an uninitialized stream.");
 
-  if (mMediaCache) {
-    return NS_OK;
-  }
-
-  NS_ASSERTION(aOriginal->mMediaCache, "Don't clone an uninitialized stream");
   // Use the same MediaCache as our clone.
   mMediaCache = aOriginal->mMediaCache;
 
   mMediaCache->OpenStream(this);
 
   mResourceID = aOriginal->mResourceID;
 
   // Grab cache blocks from aOriginal as readahead blocks for our stream
@@ -2604,18 +2600,16 @@ MediaCacheStream::InitAsClone(MediaCache
 
     while (i >= mBlocks.Length()) {
       mBlocks.AppendElement(-1);
     }
     // Every block is a readahead block for the clone because the clone's initial
     // stream offset is zero
     mMediaCache->AddBlockOwnerAsReadahead(cacheBlockIndex, this, i);
   }
-
-  return NS_OK;
 }
 
 nsresult MediaCacheStream::GetCachedRanges(MediaByteRangeSet& aRanges)
 {
   // Take the monitor, so that the cached data ranges can't grow while we're
   // trying to loop over them.
   ReentrantMonitorAutoEnter mon(mMediaCache->GetReentrantMonitor());
 

--- a/dom/media/MediaCache.h
+++ b/dom/media/MediaCache.h
@@ -200,20 +200,20 @@ public:
 
   // Set up this stream with the cache. Can fail on OOM.
   // aContentLength is the content length if known, otherwise -1.
   // Exactly one of InitAsClone or Init must be called before any other method
   // on this class. Does nothing if already initialized.
   nsresult Init(int64_t aContentLength);
 
   // Set up this stream with the cache, assuming it's for the same data
-  // as the aOriginal stream. Can fail on OOM.
+  // as the aOriginal stream.
   // Exactly one of InitAsClone or Init must be called before any other method
-  // on this class. Does nothing if already initialized.
-  nsresult InitAsClone(MediaCacheStream* aOriginal);
+  // on this class.
+  void InitAsClone(MediaCacheStream* aOriginal);
 
   // These are called on the main thread.
   // Tell us whether the stream is seekable or not. Non-seekable streams
   // will always pass 0 for aOffset to CacheClientSeek. This should only
   // be called while the stream is at channel offset 0. Seekability can
   // change during the lifetime of the MediaCacheStream --- every time
   // we do an HTTP load the seekability may be different (and sometimes
   // is, in practice, due to the effects of caching proxies).