diff --git a/pl/boot.yap b/pl/boot.yap
index a83dfabdc..1815f77f1 100644
--- a/pl/boot.yap
+++ b/pl/boot.yap
@@ -1120,7 +1120,7 @@ catch(G, C, A) :-
 %
 throw(Ball) :-
 	% get this off the unwound computation.
-	copy_term(Ball,NewBall),
+	duplicate_term(Ball,NewBall),
 	% get current jump point
 	'$jump_env_and_store_ball'(NewBall).
 
diff --git a/pl/errors.yap b/pl/errors.yap
index d82c60f9f..0d419024b 100644
--- a/pl/errors.yap
+++ b/pl/errors.yap
@@ -11,8 +11,11 @@
 * File:		errors.yap						 *
 * comments:	error messages for YAP					 *
 *									 *
-* Last rev:     $Date: 2008-03-17 12:08:28 $,$Author: vsc $						 *
+* Last rev:     $Date: 2008-04-04 10:02:44 $,$Author: vsc $						 *
 * $Log: not supported by cvs2svn $
+* Revision 1.87  2008/03/17 12:08:28  vsc
+* avoid silly message
+*
 * Revision 1.86  2008/02/23 01:32:31  vsc
 * fix chr bootstrap.
 *
@@ -205,6 +208,9 @@
 	print_message(informational,abort(user)).
 '$process_error'(abort, _) :- !,
 	throw('$abort').
+'$process_error'(error(thread_cancel(Id), G),top) :- !.
+'$process_error'(error(thread_cancel(Id), G), _) :- !,
+	throw(error(thread_cancel(Id), G)).
 '$process_error'(error(Msg, Where), _) :- !,
 	'$set_fpu_exceptions',
 	print_message(error,error(Msg, Where)).
diff --git a/pl/threads.yap b/pl/threads.yap
index 9eca1fa0b..709f10070 100644
--- a/pl/threads.yap
+++ b/pl/threads.yap
@@ -319,11 +319,7 @@ 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)),
-	'$thread_id_alias'(Id0, Id),
-	'$unlock_all_thread_mutexes'(Id0),
-	'$erase_thread_info'(Id0),
-	'$thread_destroy'(Id0).	
+	thread_signal(Id, throw(error(thread_cancel(Id),thread_cancel(Id)))).
 
 thread_detach(Id) :-
 	'$check_thread_or_alias'(Id, thread_detach(Id)),