diff --git a/.jshint b/.jshint
index 41484cf8f..871364f40 100644
--- a/.jshint
+++ b/.jshint
@@ -5,7 +5,7 @@
     "nonew": true,
     "curly": true,
     "forin": true,
-    "freeze": true,
+    "freeze": false,
     "undef": true,
     "unused": "vars"
 }
diff --git a/lib/models/room.js b/lib/models/room.js
index c9c8b4794..51554645a 100644
--- a/lib/models/room.js
+++ b/lib/models/room.js
@@ -184,7 +184,7 @@ Room.prototype.addEvents = function(events, duplicateStrategy) {
             this.currentState.setTypingEvent(events[i]);
         }
         else if (events[i].getType() === "m.receipt") {
-            addReceipt(this, events[i]);
+            this.addReceipt(events[i]);
         }
         else {
             if (duplicateStrategy) {
@@ -284,7 +284,8 @@ Room.prototype.addReceipt = function(event) {
     var self = this;
     utils.keys(event.getContent()).forEach(function(eventId) {
         utils.keys(event.getContent()[eventId]).forEach(function(receiptType) {
-            utils.keys(event.getContent()[eventId][receiptType]).forEach(function(userId) {
+            utils.keys(event.getContent()[eventId][receiptType]).forEach(
+            function(userId) {
                 var receipt = event.getContent()[eventId][receiptType][userId];
                 if (!self._receipts[receiptType]) {
                     self._receipts[receiptType] = {};
@@ -292,7 +293,6 @@ Room.prototype.addReceipt = function(event) {
                 if (!self._receipts[receiptType][userId]) {
                     self._receipts[receiptType][userId] = {};
                 }
-                var oldEventId = self._receipts[receiptType][userId].eventId;
                 self._receipts[receiptType][userId] = {
                     eventId: eventId,
                     data: receipt
diff --git a/lib/utils.js b/lib/utils.js
index 464bebc7d..2460a02fa 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -238,7 +238,6 @@ module.exports.runPolyfills = function() {
     // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
     if (!Array.prototype.filter) {
       Array.prototype.filter = function(fun/*, thisArg*/) {
-        'use strict';
 
         if (this === void 0 || this === null) {
           throw new TypeError();
@@ -282,15 +281,15 @@ module.exports.runPolyfills = function() {
 
         var T, A, k;
 
-        if (this == null) {
+        if (this === null || this === undefined) {
           throw new TypeError(' this is null or not defined');
         }
 
-        // 1. Let O be the result of calling ToObject passing the |this| 
+        // 1. Let O be the result of calling ToObject passing the |this|
         //    value as the argument.
         var O = Object(this);
 
-        // 2. Let lenValue be the result of calling the Get internal 
+        // 2. Let lenValue be the result of calling the Get internal
         //    method of O with the argument "length".
         // 3. Let len be ToUint32(lenValue).
         var len = O.length >>> 0;
@@ -306,8 +305,8 @@ module.exports.runPolyfills = function() {
           T = thisArg;
         }
 
-        // 6. Let A be a new array created as if by the expression new Array(len) 
-        //    where Array is the standard built-in constructor with that name and 
+        // 6. Let A be a new array created as if by the expression new Array(len)
+        //    where Array is the standard built-in constructor with that name and
         //    len is the value of len.
         A = new Array(len);
 
@@ -321,18 +320,18 @@ module.exports.runPolyfills = function() {
 
           // a. Let Pk be ToString(k).
           //   This is implicit for LHS operands of the in operator
-          // b. Let kPresent be the result of calling the HasProperty internal 
+          // b. Let kPresent be the result of calling the HasProperty internal
           //    method of O with argument Pk.
           //   This step can be combined with c
           // c. If kPresent is true, then
           if (k in O) {
 
-            // i. Let kValue be the result of calling the Get internal 
+            // i. Let kValue be the result of calling the Get internal
             //    method of O with argument Pk.
             kValue = O[k];
 
-            // ii. Let mappedValue be the result of calling the Call internal 
-            //     method of callback with T as the this value and argument 
+            // ii. Let mappedValue be the result of calling the Call internal
+            //     method of callback with T as the this value and argument
             //     list containing kValue, k, and O.
             mappedValue = callback.call(T, kValue, k, O);
 
@@ -363,7 +362,7 @@ module.exports.runPolyfills = function() {
         return A;
       };
     }
-}
+};
 
 /**
  * Inherit the prototype methods from one constructor into another. This is a
diff --git a/spec/unit/room.spec.js b/spec/unit/room.spec.js
index d37560599..423db86c0 100644
--- a/spec/unit/room.spec.js
+++ b/spec/unit/room.spec.js
@@ -623,5 +623,5 @@ describe("Room", function() {
 
         });
 
-    })
+    });
 });