diff --git a/content/media/nsMediaCache.cpp b/content/media/nsMediaCache.cpp
index 4fc9ae450eb..9477f8ec9b5 100644
--- a/content/media/nsMediaCache.cpp
+++ b/content/media/nsMediaCache.cpp
@@ -190,6 +190,10 @@ public:
 
   PRMonitor* Monitor() { return mMonitor; }
 
+  /**
+   * An iterator that makes it easy to iterate through all streams that
+   * have a given resource ID and are not closed.
+   */
   class ResourceStreamIterator {
   public:
     ResourceStreamIterator(PRInt64 aResourceID) :
@@ -199,7 +203,7 @@ public:
       while (mNext < gMediaCache->mStreams.Length()) {
         nsMediaCacheStream* stream = gMediaCache->mStreams[mNext];
         ++mNext;
-        if (stream->GetResourceID() == mResourceID)
+        if (stream->GetResourceID() == mResourceID && !stream->IsClosed())
           return stream;
       }
       return nsnull;