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
@@ -834,8 +834,17 @@
 		}
 		error = msleep_sbt(uq, &uc->uc_lock, PCATCH | PDROP, wmesg,
 		    sbt, 0, flags);
+retrylock:
 		uc = umtxq_getchain(&uq->uq_key);
 		mtx_lock(&uc->uc_lock);
+		if (__predict_false(uc != umtxq_getchain(&uq->uq_key))) {
+			/*
+			 * Deal with race with umtxq_requeue().  It holds
+			 * both the old lock and the new lock.
+			 */
+			mtx_unlock(&uc->uc_lock);
+			goto retrylock;
+		}
 		if (error == EINTR || error == ERESTART)
 			break;
 		if (error == EWOULDBLOCK && (flags & C_ABSOLUTE) != 0) {