diff --git a/doc/polyfill.md b/doc/polyfill.md
index 47bbbcd521..631f9adb73 100644
--- a/doc/polyfill.md
+++ b/doc/polyfill.md
@@ -1,11 +1,12 @@
 # Polyfill
 
-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).
+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.
 
 This will emulate a full ES6 environment. This polyfill is automatically loaded
-when using [6to5-node](usage.md#node) and [6to5/register](usage.md#register-hook).
+when using [6to5-node](usage.md#node).
 
 ## Usage
 
diff --git a/lib/6to5/polyfill.js b/lib/6to5/polyfill.js
index 7fe5f07da6..f6253cf6e9 100644
--- a/lib/6to5/polyfill.js
+++ b/lib/6to5/polyfill.js
@@ -1,16 +1,53 @@
 /* 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");
-ensureSymbol("hasInstance");
-ensureSymbol("isConcatSpreadable");
-ensureSymbol("isRegExp");
-ensureSymbol("toPrimitive");
-ensureSymbol("toStringTag");
-ensureSymbol("unscopables");
+
+// 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);
+}