diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
--- a/sys/kern/kern_umtx.c
+++ b/sys/kern/kern_umtx.c
@@ -706,6 +706,7 @@
 {
 	struct bintime bt, bbt;
 	struct timespec tts;
+	sbintime_t rem;
 
 	switch (timo->clockid) {
 
@@ -738,14 +739,24 @@
 			return (0);
 		}
 		*sbt = bttosbt(bt);
+
+		/*
+		 * Check if the absolute time should be aligned to
+		 * avoid firing multiple timer events in non-periodic
+		 * timer mode.
+		 */
 		switch (timo->clockid) {
 		case CLOCK_REALTIME_FAST:
 		case CLOCK_MONOTONIC_FAST:
 		case CLOCK_UPTIME_FAST:
-			*sbt += tc_tick_sbt;
+			rem = *sbt % tc_tick_sbt;
+			if (__predict_true(rem != 0))
+				*sbt += tc_tick_sbt - rem;
 			break;
 		case CLOCK_SECOND:
-			*sbt += SBT_1S;
+			rem = *sbt % SBT_1S;
+			if (__predict_true(rem != 0))
+				*sbt += SBT_1S - rem;
 			break;
 		}
 		*flags = C_ABSOLUTE;