diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 1099a76..496904b 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -948,6 +948,8 @@
 	struct nilfs_root *root;
 	int ret;
 
+	mutex_lock(&nilfs->ns_snapshot_mount_mutex);
+
 	down_read(&nilfs->ns_segctor_sem);
 	ret = nilfs_cpfile_is_snapshot(nilfs->ns_cpfile, cno);
 	up_read(&nilfs->ns_segctor_sem);
@@ -972,6 +974,7 @@
 	ret = nilfs_get_root_dentry(s, root, root_dentry);
 	nilfs_put_root(root);
  out:
+	mutex_unlock(&nilfs->ns_snapshot_mount_mutex);
 	return ret;
 }