diff --git a/packages/runtime/runtime.js b/packages/runtime/runtime.js
index 5593ca59d..47723ebea 100644
--- a/packages/runtime/runtime.js
+++ b/packages/runtime/runtime.js
@@ -82,16 +82,23 @@ var runtime = (function (exports) {
   // minifier not to mangle the names of these two functions.
   function Generator() {}
   function GeneratorFunction() {}
-  function GeneratorFunctionPrototype() {}
 
   // This is a polyfill for %IteratorPrototype% for environments that
   // don't natively support it.
-  var IteratorPrototype = {};
+  var getProto = Object.getPrototypeOf;
+  function Iterator() {
+    if (!IteratorPrototype.isPrototypeOf(this)) {
+      throw new TypeError("Iterator constructor called on non-iterator object");
+    }
+    if (getProto && getProto(this) === IteratorPrototype) {
+      throw new TypeError("Cannot instantiate abstract Iterator class");
+    }
+  }
+  var IteratorPrototype = Iterator.prototype;
   define(IteratorPrototype, iteratorSymbol, function () {
     return this;
   });
 
-  var getProto = Object.getPrototypeOf;
   var NativeIteratorPrototype = getProto && getProto(getProto(values([])));
   if (NativeIteratorPrototype &&
       NativeIteratorPrototype !== Op &&
@@ -101,17 +108,16 @@ var runtime = (function (exports) {
     IteratorPrototype = NativeIteratorPrototype;
   }
 
-  var Gp = GeneratorFunctionPrototype.prototype =
-    Generator.prototype = Object.create(IteratorPrototype);
-  GeneratorFunction.prototype = GeneratorFunctionPrototype;
-  defineProperty(Gp, "constructor", { value: GeneratorFunctionPrototype, configurable: true });
+  var Gp = Generator.prototype = Object.create(IteratorPrototype);
+  GeneratorFunction.prototype = Generator;
+  defineProperty(Gp, "constructor", { value: Generator, configurable: true });
   defineProperty(
-    GeneratorFunctionPrototype,
+    Generator,
     "constructor",
     { value: GeneratorFunction, configurable: true }
   );
   GeneratorFunction.displayName = define(
-    GeneratorFunctionPrototype,
+    Generator,
     toStringTagSymbol,
     "GeneratorFunction"
   );
@@ -138,9 +144,9 @@ var runtime = (function (exports) {
 
   exports.mark = function(genFun) {
     if (Object.setPrototypeOf) {
-      Object.setPrototypeOf(genFun, GeneratorFunctionPrototype);
+      Object.setPrototypeOf(genFun, Generator);
     } else {
-      genFun.__proto__ = GeneratorFunctionPrototype;
+      genFun.__proto__ = Generator;
       define(genFun, toStringTagSymbol, "GeneratorFunction");
     }
     genFun.prototype = Object.create(Gp);
diff --git a/test/tests.es6.js b/test/tests.es6.js
index b72ddf9cc..5a5cbac23 100644
--- a/test/tests.es6.js
+++ b/test/tests.es6.js
@@ -2625,6 +2625,9 @@ describe("generator function prototype", function() {
 
   it("should follow the expected object model", function() {
     var GeneratorFunctionPrototype = getProto(f);
+    var GeneratorPrototype = GeneratorFunctionPrototype.prototype;
+    var IteratorPrototype = getProto(GeneratorPrototype);
+    var Iterator = IteratorPrototype.constructor;
     var GeneratorFunction = GeneratorFunctionPrototype.constructor;
 
     assert.strictEqual(GeneratorFunction.name, 'GeneratorFunction');
@@ -2636,6 +2639,10 @@ describe("generator function prototype", function() {
                        getProto(f.prototype));
     assert.strictEqual(getProto(GeneratorFunctionPrototype),
                        Function.prototype);
+    assert.notStrictEqual(IteratorPrototype, Object);
+    assert.throws(() => Iterator.call({}));
+    assert.throws(() => new Iterator());
+    assert.strictEqual(f() instanceof f, true);
 
     if (typeof process === "undefined" ||
         process.version.slice(1, 3) === "0.") {