--- /app/slurm/wjb/B_2-4-0-rc1_T/src/slurmctld/preempt.c.orig	2012-05-23 11:10:33.000000000 -0700
+++ /app/slurm/wjb/B_2-4-0-rc1_T/src/slurmctld/preempt.c	2012-06-21 08:46:11.000000000 -0700
@@ -236,7 +236,7 @@
 		grace_time = qos_ptr->grace_time;
 	}
 
-	if (grace_time) {
+	if ((grace_time != NO_VAL) && (grace_time != 0)) {
 		debug("setting %u sec preemption grace time for job %u",
 		      grace_time, job_ptr->job_id);
 		_preempt_signal(job_ptr, grace_time);