diff --git a/pl/init.yap b/pl/init.yap
index 1a9deed0d..ac8347b0c 100644
--- a/pl/init.yap
+++ b/pl/init.yap
@@ -204,3 +204,5 @@ file_search_path(system, Dir) :-
 	prolog_flag(host_type, Dir).
 file_search_path(foreign, yap('lib/Yap')).
 
+%:- yap_flag(unknown,error). 
+