diff --git a/src/compiler/js-builtin-reducer.cc b/src/compiler/js-builtin-reducer.cc
index cb56f0253b..c60744c3dd 100644
--- a/src/compiler/js-builtin-reducer.cc
+++ b/src/compiler/js-builtin-reducer.cc
@@ -1451,6 +1451,7 @@ Reduction JSBuiltinReducer::ReduceCollectionIteratorNext(
     index = effect = graph()->NewNode(
         common()->Call(desc), jsgraph()->HeapConstant(callable.code()), table,
         index, jsgraph()->NoContextConstant(), effect);
+    NodeProperties::SetType(index, type_cache_.kFixedArrayLengthType);
 
     // Update the {index} and {table} on the {receiver}.
     effect = graph()->NewNode(
diff --git a/test/mjsunit/regress/regress-crbug-791245-1.js b/test/mjsunit/regress/regress-crbug-791245-1.js
new file mode 100644
index 0000000000..0d51f8a4a0
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-791245-1.js
@@ -0,0 +1,18 @@
+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+const s = new Map;
+
+function foo(s) {
+  const i = s[Symbol.iterator]();
+  i.next();
+  return i;
+}
+
+console.log(foo(s));
+console.log(foo(s));
+%OptimizeFunctionOnNextCall(foo);
+console.log(foo(s));
diff --git a/test/mjsunit/regress/regress-crbug-791245-2.js b/test/mjsunit/regress/regress-crbug-791245-2.js
new file mode 100644
index 0000000000..6734ed2baa
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-791245-2.js
@@ -0,0 +1,18 @@
+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+const s = new Set;
+
+function foo(s) {
+  const i = s[Symbol.iterator]();
+  i.next();
+  return i;
+}
+
+console.log(foo(s));
+console.log(foo(s));
+%OptimizeFunctionOnNextCall(foo);
+console.log(foo(s));