diff --git a/fs/fs.c b/fs/fs.c
index e148a07..f570312 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -258,10 +258,12 @@
 	int len_read;
 	char buf[12];
 
-	if (argc < 5)
+	if (argc < 2)
+		return CMD_RET_USAGE;
+	if (argc > 7)
 		return CMD_RET_USAGE;
 
-	if (fs_set_blk_dev(argv[1], argv[2], fstype))
+	if (fs_set_blk_dev(argv[1], (argc >= 3) ? argv[2] : NULL, fstype))
 		return 1;
 
 	if (argc >= 4) {
@@ -308,11 +310,13 @@
 {
 	if (argc < 2)
 		return CMD_RET_USAGE;
+	if (argc > 4)
+		return CMD_RET_USAGE;
 
 	if (fs_set_blk_dev(argv[1], (argc >= 3) ? argv[2] : NULL, fstype))
 		return 1;
 
-	if (fs_ls(argc == 4 ? argv[3] : "/"))
+	if (fs_ls(argc >= 4 ? argv[3] : "/"))
 		return 1;
 
 	return 0;