diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
index 951fef6cfc03..43570ce5f9be 100644
--- a/sys/kern/kern_umtx.c
+++ b/sys/kern/kern_umtx.c
@@ -2839,7 +2839,8 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct timespec *timeout)
 	umtxq_insert(uq);
 	umtxq_unlock(&uq->uq_key);
 
-	suword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 1);
+	if (fuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters)) == 0)
+		casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
 
 	count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
 	if (count != 0) {