diff --git a/dom/base/EventSource.cpp b/dom/base/EventSource.cpp
index 32329098e2..06cabc3098 100644
--- a/dom/base/EventSource.cpp
+++ b/dom/base/EventSource.cpp
@@ -190,7 +190,6 @@ public:
 
   bool IsClosed()
   {
-    MutexAutoLock lock(mMutex); 
     return ReadyState() == CLOSED;
   }