diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 7781d801212f..35e9bfcc6ad9 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -158,7 +158,8 @@ rt_mutex_waiter_less(struct rt_mutex_waiter *left,
 	 * then right waiter has a dl_prio() too.
 	 */
 	if (dl_prio(left->prio))
-		return (left->task->dl.deadline < right->task->dl.deadline);
+		return dl_time_before(left->task->dl.deadline,
+				      right->task->dl.deadline);
 
 	return 0;
 }