diff --git a/src/js/History.js b/src/js/History.js
index 64c50bc..452b1ce 100644
--- a/src/js/History.js
+++ b/src/js/History.js
@@ -38,7 +38,7 @@ History.prototype._calculateHistorySize = function () {
   var calculateItemSize = this.calculateItemSize;
   var totalSize = 0;
 
-  this.items.forEach(item => {
+  this.items.forEach(function (item) {
     totalSize += calculateItemSize(item);
   });
 
diff --git a/test/util.test.js b/test/util.test.js
index 9116338..8e272bb 100644
--- a/test/util.test.js
+++ b/test/util.test.js
@@ -93,7 +93,7 @@ describe('util', function () {
     });
 
     it('should strip MongoDB data types', function () {
-      const mongoDocument = '{\n' +
+      var mongoDocument = '{\n' +
           '   "_id" : ObjectId("123"),\n' +
           '   "isoDate" : ISODate("2012-12-19T06:01:17.171Z"),\n' +
           '   "regularNumber" : 67,\n' +
@@ -105,7 +105,7 @@ describe('util', function () {
           '   "decimal2" : NumberDecimal(4)\n' +
           '}';
 
-      const expectedJson = '{\n' +
+      var expectedJson = '{\n' +
           '   "_id" : "123",\n' +
           '   "isoDate" : "2012-12-19T06:01:17.171Z",\n' +
           '   "regularNumber" : 67,\n' +