diff --git a/doc/polyfill.md b/doc/polyfill.md
index 569d70bcd9..a97e334fb7 100644
--- a/doc/polyfill.md
+++ b/doc/polyfill.md
@@ -1,12 +1,11 @@
 # Polyfill
 
-6to5 includes a polyfill that includes the
-[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and the
-[es6-shim](https://github.com/paulmillr/es6-shim) and
-[es6-symbol](https://github.com/medikoo/es6-symbol) polyfills.
+6to5 includes a polyfill that includes a custom
+[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and
+[core.js](https://github.com/zloirock/core-js).
 
 This will emulate a full ES6 environment. This polyfill is automatically loaded
-when using [6to5-node](usage.md#node).
+when using [6to5-node](usage.md#node) and [6to5/register](usage.md#register-hook).
 
 ## Usage
 
diff --git a/lib/6to5/polyfill.js b/lib/6to5/polyfill.js
index 56142ab93b..ae3dbbe0e1 100644
--- a/lib/6to5/polyfill.js
+++ b/lib/6to5/polyfill.js
@@ -1,53 +1,2 @@
-/* jshint newcap: false, freeze: false */
-
-var ensureSymbol = function (key) {
-  Symbol[key] = Symbol[key] || Symbol(key);
-};
-
-var ensureProto = function (Constructor, key, val) {
-  var proto = Constructor.prototype;
-  if (!proto[key]) {
-    Object.defineProperty(proto, key, {
-      value: val
-    });
-  }
-};
-
-//
-
-if (typeof Symbol === "undefined") {
-  require("es6-symbol/implement");
-
-  var globSymbols = {};
-
-  Symbol.for = function (key) {
-    return globSymbols[key] = globSymbols[key] || Symbol(key);
-  };
-
-  Symbol.keyFor = function (sym) {
-    return sym.__description__;
-  };
-}
-
-require("es6-shim");
-require("regenerator/runtime");
-
-ensureSymbol("species");
-
-// Abstract references
-
-ensureSymbol("referenceGet");
-ensureSymbol("referenceSet");
-ensureSymbol("referenceDelete");
-
-ensureProto(Function, Symbol.referenceGet, function () { return this; });
-
-ensureProto(Map, Symbol.referenceGet, Map.prototype.get);
-ensureProto(Map, Symbol.referenceSet, Map.prototype.set);
-ensureProto(Map, Symbol.referenceDelete, Map.prototype.delete);
-
-if (global.WeakMap) {
-  ensureProto(WeakMap, Symbol.referenceGet, WeakMap.prototype.get);
-  ensureProto(WeakMap, Symbol.referenceSet, WeakMap.prototype.set);
-  ensureProto(WeakMap, Symbol.referenceDelete, WeakMap.prototype.delete);
-}
+require("core-js/shim");
+require("./transformation/transformers/es6-generators/runtime");
diff --git a/package.json b/package.json
index 77dcca580e..259877b7a9 100644
--- a/package.json
+++ b/package.json
@@ -39,8 +39,7 @@
     "ast-types": "~0.6.1",
     "chokidar": "0.11.1",
     "commander": "2.5.0",
-    "es6-shim": "0.21.0",
-    "es6-symbol": "0.1.1",
+    "core-js": "^0.2.2",
     "estraverse": "1.8.0",
     "esutils": "1.1.6",
     "fs-readdir-recursive": "0.1.0",
diff --git a/test/transformation.js b/test/transformation.js
index ca03b78af1..8bed3f56c1 100644
--- a/test/transformation.js
+++ b/test/transformation.js
@@ -7,6 +7,8 @@ var chai       = require("chai");
 var util       = require("../lib/6to5/util");
 var _          = require("lodash");
 
+require("../lib/6to5/polyfill");
+
 var run = function (task, done) {
   var actual = task.actual;
   var expect = task.expect;
@@ -26,8 +28,6 @@ var run = function (task, done) {
     result = transform(execCode, getOpts(exec));
     execCode = result.code;
 
-    require("../lib/6to5/polyfill");
-
     try {
       var fn = new Function("assert", "done", "genHelpers", execCode);
       fn(assert, done, genHelpers);