diff --git a/fs/namespace.c b/fs/namespace.c
index ae1463651549..c114df2f83fa 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1700,8 +1700,6 @@ static int can_umount(const struct path *path, int flags)
 {
 	struct mount *mnt = real_mount(path->mnt);
 
-	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
-		return -EINVAL;
 	if (!may_mount())
 		return -EPERM;
 	if (path->dentry != path->mnt->mnt_root)
@@ -1715,6 +1713,7 @@ static int can_umount(const struct path *path, int flags)
 	return 0;
 }
 
+// caller is responsible for flags being sane
 int path_umount(struct path *path, int flags)
 {
 	struct mount *mnt = real_mount(path->mnt);
@@ -1736,6 +1735,10 @@ int ksys_umount(char __user *name, int flags)
 	struct path path;
 	int ret;
 
+	// basic validity checks done first
+	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
+		return -EINVAL;
+
 	if (!(flags & UMOUNT_NOFOLLOW))
 		lookup_flags |= LOOKUP_FOLLOW;
 	ret = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);