diff --git a/lib/internal/iterator.js b/lib/internal/iterator.js
index 15c6fddb4..24056effd 100644
--- a/lib/internal/iterator.js
+++ b/lib/internal/iterator.js
@@ -27,6 +27,9 @@ function createObjectIterator(obj) {
     var len = okeys.length;
     return function next() {
         var key = okeys[++i];
+        if (key === '__proto__') {
+            return next();
+        }
         return i < len ? {value: obj[key], key: key} : null;
     };
 }
diff --git a/mocha_test/mapValues.js b/mocha_test/mapValues.js
index 612feffcb..640060ffd 100644
--- a/mocha_test/mapValues.js
+++ b/mocha_test/mapValues.js
@@ -39,6 +39,17 @@ describe('mapValues', function () {
                 done();
             });
         });
+
+        it('prototype pollution', (done) => {
+            var input = JSON.parse('{"a": 1, "b": 2, "__proto__": { "exploit": true }}');
+
+            async.mapValues(input, (val, key, next) => {
+                next(null, val)
+            }, (err, result) => {
+                expect(result.exploit).to.equal(undefined)
+                done(err);
+            })
+        })
     });
 
     context('mapValues', function () {