diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index 24b2845318..a11008ec26 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -36,7 +36,6 @@ var ignoreRegex   = /node_modules/;
 var onlyRegex;
 var exts          = {};
 var maps          = {};
-var old           = require.extensions[".js"];
 
 var mtime = function (filename) {
   return +fs.statSync(filename).mtime;
@@ -94,7 +93,7 @@ var registerExtension = function (ext) {
   var old = require.extensions[ext];
 
   var loader = normalLoader;
-  if (process.env.running_under_istanbul) loader = istanbulLoader;
+  if (process.env.running_under_istanbul) loader = istanbulLoader; // jshint ignore:line
 
   require.extensions[ext] = function (m, filename) {
     if (shouldIgnore(filename)) {