diff --git a/sys/kern/kern_switch.c b/sys/kern/kern_switch.c
index 917f7368256..42fee61a99a 100644
--- a/sys/kern/kern_switch.c
+++ b/sys/kern/kern_switch.c
@@ -493,7 +493,7 @@ int
 runq_findq(struct runq *const rq, const int lvl_min, const int lvl_max,
     runq_pred_t *const pred, void *const pred_data)
 {
-	rqsw_t const (*const rqsw)[RQSW_NB] = &rq->rq_status.rq_sw;
+	const rqsw_t (*const rqsw)[RQSW_NB] = &rq->rq_status.rq_sw;
 	rqsw_t w;
 	int i, last, idx;
 
@@ -568,20 +568,27 @@ runq_first_thread(struct runq *const rq)
 
 /*
  * Return true if there are some processes of any priority on the run queue,
- * false otherwise.  Has no side effects.
+ * false otherwise.  Has no side effects.  Supports racy lookups (required by
+ * 4BSD).
  */
 bool
 runq_not_empty(struct runq *rq)
 {
-	struct thread *const td = runq_first_thread(rq);
+	const rqsw_t (*const rqsw)[RQSW_NB] = &rq->rq_status.rq_sw;
+	int sw_idx;
 
-	if (td != NULL) {
-		CTR2(KTR_RUNQ, "runq_not_empty: idx=%d, td=%p",
-		    td->td_rqindex, td);
-		return (true);
+	for (sw_idx = 0; sw_idx < RQSW_NB; ++sw_idx) {
+		const rqsw_t w = (*rqsw)[sw_idx];
+
+		if (w != 0) {
+			CTR3(KTR_RUNQ, "runq_not_empty: not empty; "
+			    "rq=%p, sw_idx=%d, bits=" RQSW_PRI,
+			    rq, sw_idx, w);
+			return (true);
+		}
 	}
 
-	CTR0(KTR_RUNQ, "runq_not_empty: empty");
+	CTR1(KTR_RUNQ, "runq_not_empty: empty; rq=%p", rq);
 	return (false);
 }