diff --git a/pl/threads.yap b/pl/threads.yap
index 9db283677..b2084ca38 100644
--- a/pl/threads.yap
+++ b/pl/threads.yap
@@ -247,7 +247,9 @@ thread_join(Id, Status) :-
 	'$erase_thread_info'(Id0),
 	'$thread_destroy'(Id0).
 
-
+thread_cancel(Id) :-
+	(Id == main; Id == 0), !,
+	'$do_error'(permission_error(cancel, thread, main), thread_cancel(Id)).
 thread_cancel(Id) :-
 	'$check_thread_or_alias'(Id, thread_cancel(Id)),
 	'$thread_id_alias'(Id0, Id),