--- b/sys/kern/kern_sig.c	
+++ b/sys/kern/kern_sig.c	
@@ -2370,7 +2370,8 @@ tdsigwakeup(struct thread *td, int sig, sig_t action, int intrval)
 	 * Bring the priority of a thread up if we want it to get
 	 * killed in this lifetime.
 	 */
-	if (action == SIG_DFL && (prop & SA_KILL) && td->td_priority > PUSER)
+	if (action == SIG_DFL && (prop & SA_KILL) != 0 &&
+	    td->td_priority > PUSER && !TD_IS_IDLETHREAD(td))
 		sched_prio(td, PUSER);
 	if (TD_ON_SLEEPQ(td)) {
 		/*