--- libaitsched/src/hooks.c	2014/05/21 20:48:34	1.27.2.1
+++ libaitsched/src/hooks.c	2014/05/21 21:55:10	1.27.2.2
@@ -3,7 +3,7 @@
 *  by Michael Pounov <misho@openbsd-bg.org>
 *
 * $Author: misho $
-* $Id: hooks.c,v 1.27.2.1 2014/05/21 20:48:34 misho Exp $
+* $Id: hooks.c,v 1.27.2.2 2014/05/21 21:55:10 misho Exp $
 *
 **************************************************************************
 The ELWIX and AITNET software is distributed under the following
@@ -267,7 +267,8 @@ sched_hook_cancel(void *task, void *arg __unused)
 #endif	/* EVFILT_USER */
 		case taskTHREAD:
 #ifdef HAVE_LIBPTHREAD
-			pthread_cancel((pthread_t) TASK_VAL(t));
+			if (TASK_VAL(t))
+				pthread_cancel((pthread_t) TASK_VAL(t));
 #endif
 			return NULL;
 #if defined(HAVE_TIMER_CREATE) && defined(HAVE_TIMER_SETTIME) && defined(HAVE_TIMER_DELETE)