diff --git a/spec/core/matchers/matchersUtilSpec.js b/spec/core/matchers/matchersUtilSpec.js
index 3a8054a7..1e1140e2 100644
--- a/spec/core/matchers/matchersUtilSpec.js
+++ b/spec/core/matchers/matchersUtilSpec.js
@@ -413,6 +413,53 @@ describe("matchersUtil", function() {
       var setB = new Set([6, 3]);
       expect(jasmineUnderTest.matchersUtil.equals(setA, setB)).toBe(false);
     });
+
+    describe("when running in an environment with array polyfills", function() {
+      // IE 8 doesn't support `definePropery` on non-DOM nodes
+      if (jasmine.getEnv().ieVersion < 9) { return; }
+
+      var findIndexDescriptor = Object.getOwnPropertyDescriptor(Array.prototype, 'findIndex');
+      if (!findIndexDescriptor) {
+        return;
+      }
+
+      beforeEach(function() {
+        Object.defineProperty(Array.prototype, 'findIndex', {
+          enumerable: true,
+          value: function (predicate) {
+	            if (this === null) {
+	                throw new TypeError('Array.prototype.findIndex called on null or undefined');
+	            }
+
+	            if (typeof predicate !== 'function') {
+	                throw new TypeError('predicate must be a function');
+	            }
+
+	            var list = Object(this);
+	            var length = list.length >>> 0;
+	            var thisArg = arguments[1];
+	            var value;
+
+	            for (var i = 0; i < length; i++) {
+	                value = list[i];
+	                if (predicate.call(thisArg, value, i, list)) {
+	                    return i;
+	                }
+	            }
+
+	            return -1;
+	        }
+        });
+      });
+
+      afterEach(function() {
+        Object.defineProperty(Array.prototype, 'findIndex', findIndexDescriptor);
+      });
+
+      it("passes when there's an array polyfill", function() {
+        expect(['foo']).toEqual(['foo']);
+      });
+    });
   });
 
   describe("contains", function() {
diff --git a/src/core/matchers/matchersUtil.js b/src/core/matchers/matchersUtil.js
index 28314891..3aba3f0f 100644
--- a/src/core/matchers/matchersUtil.js
+++ b/src/core/matchers/matchersUtil.js
@@ -327,7 +327,7 @@ getJasmineRequireObj().matchersUtil = function(j$) {
     }
 
     var extraKeys = [];
-    for (var i in allKeys) {
+    for (var i = 0; i < allKeys.length; i++) {
       if (!allKeys[i].match(/^[0-9]+$/)) {
         extraKeys.push(allKeys[i]);
       }