diff --git a/index.js b/index.js
index a6f40c7..ad529ce 100644
--- a/index.js
+++ b/index.js
@@ -33,7 +33,7 @@ module.exports = function (obj, opts) {
         if (typeof node !== 'object' || node === null) {
             return JSON.stringify(node);
         }
-        if (isArray(node)) {
+        if (Array.isArray(node)) {
             var out = [];
             for (var i = 0; i < node.length; i++) {
                 var item = stringify(node, i, node[i], level+1) || JSON.stringify(null);
@@ -48,7 +48,7 @@ module.exports = function (obj, opts) {
             }
             else seen.push(node);
 
-            var keys = objectKeys(node).sort(cmp && cmp(node));
+            var keys = Object.keys(node).sort(cmp && cmp(node));
             var out = [];
             for (var i = 0; i < keys.length; i++) {
                 var key = keys[i];
@@ -67,16 +67,3 @@ module.exports = function (obj, opts) {
         }
     })({ '': obj }, '', obj, 0);
 };
-
-var isArray = Array.isArray || function (x) {
-    return {}.toString.call(x) === '[object Array]';
-};
-
-var objectKeys = Object.keys || function (obj) {
-    var has = Object.prototype.hasOwnProperty || function () { return true };
-    var keys = [];
-    for (var key in obj) {
-        if (has.call(obj, key)) keys.push(key);
-    }
-    return keys;
-};
diff --git a/package.json b/package.json
index 2184fea..3b48917 100644
--- a/package.json
+++ b/package.json
@@ -14,7 +14,7 @@
   "testling": {
     "files": "test/*.js",
     "browsers": [
-      "ie/8..latest",
+      "ie/9..latest",
       "ff/5", "ff/latest",
       "chrome/15", "chrome/latest",
       "safari/latest",