--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1656,8 +1656,10 @@ static int do_move_mount(struct path *pa
 
 	/* moving to or from a union mount is not supported */
 	err = -EINVAL;
+#if 0
 	if (IS_MNT_UNION(path->mnt))
 		goto exit;
+#endif
 	if (IS_MNT_UNION(old_path.mnt))
 		goto exit;
 
--- a/fs/union.c
+++ b/fs/union.c
@@ -260,8 +260,6 @@ int append_to_union(struct vfsmount *mnt
 	spin_lock(&union_lock);
 	um = union_lookup(dentry, mnt);
 	if (um) {
-		BUG_ON((um->u_next.dentry != dest_dentry) ||
-		       (um->u_next.mnt != dest_mnt));
 		spin_unlock(&union_lock);
 		union_put(this);
 		return 0;
@@ -274,6 +272,23 @@ int append_to_union(struct vfsmount *mnt
 	return 0;
 }
 
+int follow_union_mountpoint(struct path *path)
+{
+	struct path new_path = *path;
+
+	path_get(&new_path);
+	while (follow_union_down(&new_path)) {
+		if (new_path.dentry != new_path.mnt->mnt_root)
+			continue;
+
+		path_put(path);
+		*path = new_path;
+		return 1;
+	}
+	path_put(&new_path);
+	return 0;
+}
+
 /*
  * follow_union_down - follow the union stack one layer down
  *
--- a/include/linux/union.h
+++ b/include/linux/union.h
@@ -47,6 +47,7 @@ extern int append_to_union(struct vfsmou
 			   struct vfsmount *, struct dentry *);
 extern int follow_union_down(struct path *);
 extern int follow_union_mount(struct path *);
+extern int follow_union_mountpoint(struct path *path);
 extern void __d_drop_unions(struct dentry *);
 extern void shrink_d_unions(struct dentry *);
 extern void __shrink_d_unions(struct dentry *, struct list_head *);
@@ -68,6 +69,7 @@ extern int union_permission(struct path 
 #define append_to_union(x1, y1, x2, y2)	({ BUG(); (0); })
 #define follow_union_down(x)		({ (0); })
 #define follow_union_mount(x)	({ (0); })
+#define follow_union_mountpoint(x)	({ (0); })
 #define __d_drop_unions(x)		do { } while (0)
 #define shrink_d_unions(x)		do { } while (0)
 #define __shrink_d_unions(x,y)		do { } while (0)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -626,6 +626,9 @@ static int cache_lookup_union(struct nam
 		    !S_ISDIR(path->dentry->d_inode->i_mode))
 			goto out;
 
+		if (follow_union_mountpoint(path))
+			goto out;
+
 		/* Build the union stack for this part */
 		res = __cache_lookup_build_union(nd, name, path);
 		if (res) {
@@ -892,6 +895,9 @@ static int real_lookup_union(struct name
 	    !S_ISDIR(path->dentry->d_inode->i_mode))
 		goto out;
 
+	if (follow_union_mountpoint(path))
+		goto out;
+
 	/* Build the union stack for this part */
 	res = __real_lookup_build_union(nd, name, path);
 	if (res) {
@@ -1813,6 +1819,9 @@ int hash_lookup_union(struct nameidata *
 	    !S_ISDIR(path->dentry->d_inode->i_mode))
 		goto out;
 
+	if (follow_union_mountpoint(path))
+		goto out;
+
 	/* Build the union stack for this part */
 	res = __hash_lookup_build_union(nd, name, path);
 	if (res) {
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -17,6 +17,7 @@
 #include <linux/syscalls.h>
 #include <linux/unistd.h>
 #include <linux/union.h>
+#include <linux/mount.h>
 
 #include <asm/uaccess.h>
 
@@ -45,7 +46,7 @@ int vfs_readdir(struct file *file, filld
 		 * below this one in the union stack.
 		 */
 		if (is_unionized(file->f_path.dentry, file->f_path.mnt) &&
-		    !IS_OPAQUE(inode)) {
+		    !IS_OPAQUE(inode) && IS_MNT_UNION(file->f_path.mnt)) {
 			res = union_copyup_dir(&file->f_path);
 			if (res)
 				goto out_unlock;