diff --git a/sys/fs/union/union.h b/sys/fs/union/union.h
index a08a689c7e3b..f1c9e048136f 100644
--- a/sys/fs/union/union.h
+++ b/sys/fs/union/union.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: union.h,v 1.29 2017/07/17 09:22:36 hannken Exp $	*/
+/*	$NetBSD: union.h,v 1.29.10.1 2020/08/27 09:08:39 martin Exp $	*/
 
 /*
  * Copyright (c) 1994 The Regents of the University of California.
@@ -130,6 +130,7 @@ struct union_node {
 	char			*un_path;	/* v: saved component name */
 	int			un_openl;	/* v: # of opens on lowervp */
 	unsigned int		un_cflags;	/* c: cache flags */
+	bool			un_hooknode;	/* :: from union_readdirhook */
 	struct vnode		**un_dircache;	/* v: cached union stack */
 	off_t			un_uppersz;	/* l: size of upper object */
 	off_t			un_lowersz;	/* l: size of lower object */
diff --git a/sys/fs/union/union_subr.c b/sys/fs/union/union_subr.c
index 30c481a5c4b9..6bab6cf2df5e 100644
--- a/sys/fs/union/union_subr.c
+++ b/sys/fs/union/union_subr.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: union_subr.c,v 1.77 2018/01/28 15:48:44 christos Exp $	*/
+/*	$NetBSD: union_subr.c,v 1.77.8.1 2020/08/27 09:08:39 martin Exp $	*/
 
 /*
  * Copyright (c) 1994
@@ -72,7 +72,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: union_subr.c,v 1.77 2018/01/28 15:48:44 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: union_subr.c,v 1.77.8.1 2020/08/27 09:08:39 martin Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -479,6 +479,7 @@ found:
 	un->un_dircache = 0;
 	un->un_openl = 0;
 	un->un_cflags = 0;
+	un->un_hooknode = false;
 
 	un->un_uppersz = VNOVAL;
 	un->un_lowersz = VNOVAL;
@@ -1065,7 +1066,7 @@ union_dircache(struct vnode *vp, struct lwp *l)
 	} else {
 		vpp = dircache;
 		do {
-			if (*vpp++ == VTOUNION(vp)->un_uppervp)
+			if (*vpp++ == VTOUNION(vp)->un_lowervp)
 				break;
 		} while (*vpp != NULLVP);
 	}
@@ -1074,10 +1075,12 @@ union_dircache(struct vnode *vp, struct lwp *l)
 		goto out;
 
 	vref(*vpp);
-	error = union_allocvp(&nvp, vp->v_mount, NULLVP, NULLVP, 0, *vpp, NULLVP, 0);
+	error = union_allocvp(&nvp, vp->v_mount, NULLVP, NULLVP, 0,
+	    NULLVP, *vpp, 0);
 	if (!error) {
 		vn_lock(nvp, LK_EXCLUSIVE | LK_RETRY);
 		VTOUNION(vp)->un_dircache = 0;
+		VTOUNION(nvp)->un_hooknode = true;
 		VTOUNION(nvp)->un_dircache = dircache;
 	}
 
diff --git a/sys/fs/union/union_vnops.c b/sys/fs/union/union_vnops.c
index 7593ccc1150e..c18981b9019a 100644
--- a/sys/fs/union/union_vnops.c
+++ b/sys/fs/union/union_vnops.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: union_vnops.c,v 1.70 2017/05/26 14:21:01 riastradh Exp $	*/
+/*	$NetBSD: union_vnops.c,v 1.70.14.1 2020/08/27 09:08:39 martin Exp $	*/
 
 /*
  * Copyright (c) 1992, 1993, 1994, 1995
@@ -72,7 +72,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: union_vnops.c,v 1.70 2017/05/26 14:21:01 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: union_vnops.c,v 1.70.14.1 2020/08/27 09:08:39 martin Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -1492,13 +1492,29 @@ union_readdir(void *v)
 		int a_ncookies;
 	} */ *ap = v;
 	struct union_node *un = VTOUNION(ap->a_vp);
-	struct vnode *uvp = un->un_uppervp;
+	struct vnode *vp;
+	int dolock, error;
 
-	if (uvp == NULLVP)
-		return (0);
+	if (un->un_hooknode) {
+		KASSERT(un->un_uppervp == NULLVP);
+		KASSERT(un->un_lowervp != NULLVP);
+		vp = un->un_lowervp;
+		dolock = 1;
+	} else {
+		vp = un->un_uppervp;
+		dolock = 0;
+	}
+	if (vp == NULLVP)
+		return 0;
 
-	ap->a_vp = uvp;
-	return (VCALL(uvp, VOFFSET(vop_readdir), ap));
+	if (dolock)
+		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+	ap->a_vp = vp;
+	error = VCALL(vp, VOFFSET(vop_readdir), ap);
+	if (dolock)
+		VOP_UNLOCK(vp);
+
+	return error;
 }
 
 int