diff --git a/sys/kern/kern_sleepq.c b/sys/kern/kern_sleepq.c
index 9cc05651e9d6..9b084d617328 100644
--- a/sys/kern/kern_sleepq.c
+++ b/sys/kern/kern_sleepq.c
@@ -335,6 +335,15 @@ sleepq_block(int timo, bool catch_p)
 	if (early) {
 		/* lwp_unsleep() will release the lock */
 		lwp_unsleep(l, true);
+		if (__predict_false(biglocks != 0)) {
+			KASSERTMSG(biglocks == l->l_biglocks,
+			    "reentered l_biglocks=%d biglocks=%d",
+			    l->l_biglocks, biglocks);
+			KERNEL_LOCK(biglocks, NULL);
+		}
+		l->l_biglocks = -1;
+		KASSERTMSG(biglocks == curlwp->l_blcnt,
+		    "slipped %d->%d biglocks", biglocks, curlwp->l_blcnt);
 	} else {
 		/*
 		 * The LWP may have already been awoken if the caller
@@ -349,6 +358,15 @@ sleepq_block(int timo, bool catch_p)
 		}
 		spc_lock(l->l_cpu);
 		mi_switch(l);
+		if (__predict_false(biglocks != 0)) {
+			KASSERTMSG(biglocks == l->l_biglocks,
+			    "reentered l_biglocks=%d biglocks=%d",
+			    l->l_biglocks, biglocks);
+			KERNEL_LOCK(biglocks, NULL);
+		}
+		l->l_biglocks = -1;
+		KASSERTMSG(biglocks == curlwp->l_blcnt,
+		    "slipped %d->%d biglocks", biglocks, curlwp->l_blcnt);
 
 		/* The LWP and sleep queue are now unlocked. */
 		if (timo) {
@@ -361,9 +379,14 @@ sleepq_block(int timo, bool catch_p)
 			 * co-located on the CPU with the LWP.
 			 */
 			(void)callout_halt(&l->l_timeout_ch, NULL);
+			KASSERTMSG(biglocks == curlwp->l_blcnt,
+			    "slipped %d->%d biglocks",
+			    biglocks, curlwp->l_blcnt);
 			error = (l->l_flag & LW_STIMO) ? EWOULDBLOCK : 0;
 		}
 	}
+	KASSERTMSG(biglocks == curlwp->l_blcnt,
+	    "slipped %d->%d biglocks", biglocks, curlwp->l_blcnt);
 
 	/*
 	 * LW_CATCHINTR is only modified in this function OR when we
@@ -394,13 +417,15 @@ sleepq_block(int timo, bool catch_p)
 			    (sig = issignal(l)) != 0)
 				error = sleepq_sigtoerror(l, sig);
 			mutex_exit(p->p_lock);
+			KASSERTMSG(biglocks == curlwp->l_blcnt,
+			    "slipped %d->%d biglocks",
+			    biglocks, curlwp->l_blcnt);
 		}
 	}
 
 	ktrcsw(0, 0);
-	if (__predict_false(biglocks != 0)) {
-		KERNEL_LOCK(biglocks, NULL);
-	}
+	KASSERTMSG(biglocks == curlwp->l_blcnt,
+	    "slipped %d->%d biglocks", biglocks, curlwp->l_blcnt);
 	return error;
 }