Index: linux-2.6.15.3/kernel/sched.c
===================================================================
--- linux-2.6.15.3.orig/kernel/sched.c	2006-04-19 11:07:51.000000000 +0200
+++ linux-2.6.15.3/kernel/sched.c	2006-04-19 23:14:43.000000000 +0200
@@ -5779,7 +5779,7 @@ int ipipe_setscheduler_root (struct task
 	runqueue_t *rq;
 	int oldprio;
 
-	if (prio < 1 || prio > MAX_RT_PRIO-1)
+	if (prio < 0 || prio > MAX_RT_PRIO-1)
 		return -EINVAL;
 
 	rq = task_rq_lock(p, &flags);