diff --git a/shell.c b/shell.c
index ace62e4b65..c3bf8ec38a 100644
--- a/shell.c
+++ b/shell.c
@@ -13,7 +13,7 @@ static int do_generic_cmd(const char *me, char *arg)
 	const char *my_argv[4];
 
 	setup_path();
-	if (!arg || !(arg = sq_dequote(arg)))
+	if (!arg || !(arg = sq_dequote(arg)) || *arg == '-')
 		die("bad argument");
 	if (!starts_with(me, "git-"))
 		die("bad command");