diff --git a/mozilla/xpcom/io/nsDirectoryService.cpp b/mozilla/xpcom/io/nsDirectoryService.cpp
index 72613e2edbd..e2232023d67 100644
--- a/mozilla/xpcom/io/nsDirectoryService.cpp
+++ b/mozilla/xpcom/io/nsDirectoryService.cpp
@@ -476,7 +476,7 @@ nsDirectoryService::~nsDirectoryService()
 
 }
 
-NS_IMPL_ISUPPORTS3(nsDirectoryService, nsIProperties, nsIDirectoryService, nsIDirectoryServiceProvider)
+NS_IMPL_THREADSAFE_ISUPPORTS3(nsDirectoryService, nsIProperties, nsIDirectoryService, nsIDirectoryServiceProvider)
 
 
 NS_IMETHODIMP