diff --git a/lib/system/has-flag.js b/lib/system/has-flag.js
index e70d7db..84958fa 100644
--- a/lib/system/has-flag.js
+++ b/lib/system/has-flag.js
@@ -12,6 +12,7 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
 
 'use strict';
 module.exports = function (flag, argv) {
+	argv = argv || process.argv;
 	var terminatorPos = argv.indexOf('--');
  	var prefix = /^-{1,2}/.test(flag) ? '' : '--';
 	var pos = argv.indexOf(prefix + flag);