diff --git a/pl/modules.yap b/pl/modules.yap
index 439a10487..ebe20ffb4 100644
--- a/pl/modules.yap
+++ b/pl/modules.yap
@@ -514,7 +514,7 @@ source_module(Mod) :-
 	use_module(:,?),
 	use_module(?,:,?),
 	when(?,:),
-	with_mutex(?,:),
+	with_mutex(+,:),
 	^(+,:),
 	\+ : .