diff --git a/sys/fs/nullfs/null_vnops.c b/sys/fs/nullfs/null_vnops.c
--- a/sys/fs/nullfs/null_vnops.c
+++ b/sys/fs/nullfs/null_vnops.c
@@ -385,7 +385,7 @@
 {
 	struct componentname *cnp = ap->a_cnp;
 	struct vnode *dvp = ap->a_dvp;
-	int flags = cnp->cn_flags;
+	uint64_t flags = cnp->cn_flags, old_cm;
 	struct vnode *vp, *ldvp, *lvp;
 	struct mount *mp;
 	int error;
@@ -411,8 +411,8 @@
 	 */
 	if ((ldvp->v_vflag & VV_ROOT) != 0 && (flags & ISDOTDOT) != 0) {
 		KASSERT((dvp->v_vflag & VV_ROOT) == 0,
-		    ("ldvp %p fl %#x dvp %p fl %#x flags %#x",
-		    ldvp, ldvp->v_vflag, dvp, dvp->v_vflag, flags));
+		    ("ldvp %p fl %#x dvp %p fl %#x flags %#jx",
+		    ldvp, ldvp->v_vflag, dvp, dvp->v_vflag, (uintmax_t)flags));
 		return (ENOENT);
 	}
 
@@ -423,7 +423,10 @@
 	 */
 	vhold(ldvp);
 
+	old_cm = ~NOCROSSMOUNT | (flags & NOCROSSMOUNT);
+	cnp->cn_flags |= NOCROSSMOUNT;
 	error = VOP_LOOKUP(ldvp, &lvp, cnp);
+	cnp->cn_flags &= old_cm;
 
 	/*
 	 * VOP_LOOKUP() on lower vnode may unlock ldvp, which allows