diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index 06a63497f539..aea994f036bb 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -751,14 +751,12 @@ static void
 filt_timerdetach(struct knote *kn)
 {
 	struct kq_timer_cb_data *kc;
-#ifdef INVARIANTS
-	unsigned int old;
-#endif
+	unsigned int old __unused;
 
 	kc = kn->kn_ptr.p_v;
 	callout_drain(&kc->c);
 	free(kc, M_KQUEUE);
-	DBGSET(old, atomic_fetchadd_int(&kq_ncallouts, -1));
+	old = atomic_fetchadd_int(&kq_ncallouts, -1);
 	KASSERT(old > 0, ("Number of callouts cannot become negative"));
 	kn->kn_status |= KN_DETACHED;	/* knlist_remove sets it */
 }