diff --git a/parser/html/nsHtml5OwningUTF16Buffer.h b/parser/html/nsHtml5OwningUTF16Buffer.h
index d7e3200ea..0d8777464 100644
--- a/parser/html/nsHtml5OwningUTF16Buffer.h
+++ b/parser/html/nsHtml5OwningUTF16Buffer.h
@@ -52,7 +52,7 @@ public:
     nsrefcnt AddRef();
     nsrefcnt Release();
   private:
-    nsAutoRefCnt mRefCnt;
+    mozilla::ThreadSafeAutoRefCnt mRefCnt;
 };
 
 #endif // nsHtml5OwningUTF16Buffer_h