diff --git a/pgcs/main.py b/pgcs/main.py
index 3550c55..730f628 100644
--- a/pgcs/main.py
+++ b/pgcs/main.py
@@ -13,6 +13,7 @@ def main() -> None:
     parser_traverse = subparsers.add_parser(
         "traverse", help="default positional argument `pg` == `pg traverse`"
     )
+    parser_traverse.add_argument("root", nargs="?")
     parser_pref = subparsers.add_parser("pref", help="set pref")
     parser_pref.add_argument("--init", action="store_true")
     parser_pref.add_argument("key", nargs="?")