diff --git a/lib/helper.js b/lib/helper.js
index e59e06b1..08f4e90a 100644
--- a/lib/helper.js
+++ b/lib/helper.js
@@ -84,7 +84,8 @@ exports.formatArgs = function* (cwd, args, options) {
   return args;
 };
 
-exports.formatExecArgv = function(args = []) {
+exports.formatExecArgv = function(args) {
+  args = args || [];
   return process.execArgv.concat(args.filter(passbyArgv));
 };