diff --git a/storage/src/mozStorageConnection.cpp b/storage/src/mozStorageConnection.cpp
index 07e3c94c5ca4..da19f6e01543 100644
--- a/storage/src/mozStorageConnection.cpp
+++ b/storage/src/mozStorageConnection.cpp
@@ -1054,6 +1054,7 @@ Connection::Clone(bool aReadOnly,
   }
 
   // Copy any functions that have been added to this connection.
+  SQLiteMutexAutoLock lockedScope(sharedDBMutex);
   (void)mFunctions.EnumerateRead(copyFunctionEnumerator, clone);
 
   NS_ADDREF(*_connection = clone);