diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 70aef327b6e8..015d432bcb08 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -573,7 +573,7 @@ static void alarm_timer_get(struct k_itimer *timr,
 static int alarm_timer_del(struct k_itimer *timr)
 {
 	if (!rtcdev)
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 
 	if (alarm_try_to_cancel(&timr->it.alarm.alarmtimer) < 0)
 		return TIMER_RETRY;
@@ -597,7 +597,7 @@ static int alarm_timer_set(struct k_itimer *timr, int flags,
 	ktime_t exp;
 
 	if (!rtcdev)
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;
 
 	if (flags & ~TIMER_ABSTIME)
 		return -EINVAL;