diff --git a/netwerk/cache/filecache/nsDiskCacheRecordChannel.cpp b/netwerk/cache/filecache/nsDiskCacheRecordChannel.cpp
index b2b735a96cd..eaec8145af1 100644
--- a/netwerk/cache/filecache/nsDiskCacheRecordChannel.cpp
+++ b/netwerk/cache/filecache/nsDiskCacheRecordChannel.cpp
@@ -63,7 +63,7 @@ class WriteStreamWrapper : public nsIOutputStream
 };
 
 // implement nsISupports
-NS_IMPL_ISUPPORTS(WriteStreamWrapper, NS_GET_IID(nsIOutputStream))
+NS_IMPL_THREADSAFE_ISUPPORTS(WriteStreamWrapper, NS_GET_IID(nsIOutputStream))
 
 WriteStreamWrapper::WriteStreamWrapper(nsDiskCacheRecordChannel* aChannel, 
                                        nsIOutputStream *aBaseStream)