diff --git a/lib/unexpected.js b/lib/unexpected.js
index 328ed96de..24976c0c6 100644
--- a/lib/unexpected.js
+++ b/lib/unexpected.js
@@ -37,16 +37,29 @@
                 return true;
             },
 
-            indexOf: function (arr, o, i) {
-                if (arr.length === undefined) {
-                    return -1;
+            indexOf: function (arr, searchElement, fromIndex) {
+                var length = arr.length >>> 0; // Hack to convert object.length to a UInt32
+
+                fromIndex = +fromIndex || 0;
+
+                if (Math.abs(fromIndex) === Infinity) {
+                    fromIndex = 0;
+                }
+
+                if (fromIndex < 0) {
+                    fromIndex += length;
+                    if (fromIndex < 0) {
+                        fromIndex = 0;
+                    }
                 }
 
-                for (var j = arr.length, k = k < 0 ? k + j < 0 ? 0 : k + j : k || 0; k < j && arr[k] !== o; k += 1) {
-                    // Looping
+                for (;fromIndex < length; fromIndex += 1) {
+                    if (arr[fromIndex] === searchElement) {
+                        return fromIndex;
+                    }
                 }
 
-                return j <= i ? -1 : i;
+                return -1;
             },
 
             getKeys: function (obj) {