diff --git a/dirname.c b/dirname.c
index 8392bc0..45e1a7e 100644
--- a/dirname.c
+++ b/dirname.c
@@ -13,7 +13,10 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (argc != 1)
 		usage();