diff --git a/doc/polyfill.md b/doc/polyfill.md
index 631f9adb73..47bbbcd521 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 f6253cf6e9..7fe5f07da6 100644
--- a/lib/6to5/polyfill.js
+++ b/lib/6to5/polyfill.js
@@ -1,53 +1,16 @@
 /* jshint newcap: false, freeze: false */
 
+require("core-js/shim");
+require("./transformation/transformers/es6-generators/runtime");
+
 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("./transformation/transformers/es6-generators/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);
-}
+ensureSymbol("hasInstance");
+ensureSymbol("isConcatSpreadable");
+ensureSymbol("isRegExp");
+ensureSymbol("toPrimitive");
+ensureSymbol("toStringTag");
+ensureSymbol("unscopables");