diff --git a/src/SecondLevelDomains.js b/src/SecondLevelDomains.js
index 6cac8b8..8ba2503 100644
--- a/src/SecondLevelDomains.js
+++ b/src/SecondLevelDomains.js
@@ -29,9 +29,9 @@
   'use strict';
 
   // save current SecondLevelDomains variable, if any
-  var _SecondLevelDomains = root && root.SecondLevelDomains;
+  let _SecondLevelDomains = root && root.SecondLevelDomains;
 
-  var SLD = {
+  let SLD = {
     // list of known Second Level Domains
     // converted list of SLDs from https://github.com/gavingmiller/second-level-domains
     // ----
@@ -186,45 +186,45 @@
     // Following methods use lastIndexOf() rather than array.split() in order
     // to avoid any memory allocations.
     has: function(domain) {
-      var tldOffset = domain.lastIndexOf('.');
+      let tldOffset = domain.lastIndexOf('.');
       if (tldOffset <= 0 || tldOffset >= (domain.length-1)) {
         return false;
       }
-      var sldOffset = domain.lastIndexOf('.', tldOffset-1);
+      let sldOffset = domain.lastIndexOf('.', tldOffset-1);
       if (sldOffset <= 0 || sldOffset >= (tldOffset-1)) {
         return false;
       }
-      var sldList = SLD.list[domain.slice(tldOffset+1)];
+      let sldList = SLD.list[domain.slice(tldOffset+1)];
       if (!sldList) {
         return false;
       }
       return sldList.indexOf(' ' + domain.slice(sldOffset+1, tldOffset) + ' ') >= 0;
     },
     is: function(domain) {
-      var tldOffset = domain.lastIndexOf('.');
+      let tldOffset = domain.lastIndexOf('.');
       if (tldOffset <= 0 || tldOffset >= (domain.length-1)) {
         return false;
       }
-      var sldOffset = domain.lastIndexOf('.', tldOffset-1);
+      let sldOffset = domain.lastIndexOf('.', tldOffset-1);
       if (sldOffset >= 0) {
         return false;
       }
-      var sldList = SLD.list[domain.slice(tldOffset+1)];
+      let sldList = SLD.list[domain.slice(tldOffset+1)];
       if (!sldList) {
         return false;
       }
       return sldList.indexOf(' ' + domain.slice(0, tldOffset) + ' ') >= 0;
     },
     get: function(domain) {
-      var tldOffset = domain.lastIndexOf('.');
+      let tldOffset = domain.lastIndexOf('.');
       if (tldOffset <= 0 || tldOffset >= (domain.length-1)) {
         return null;
       }
-      var sldOffset = domain.lastIndexOf('.', tldOffset-1);
+      let sldOffset = domain.lastIndexOf('.', tldOffset-1);
       if (sldOffset <= 0 || sldOffset >= (tldOffset-1)) {
         return null;
       }
-      var sldList = SLD.list[domain.slice(tldOffset+1)];
+      let sldList = SLD.list[domain.slice(tldOffset+1)];
       if (!sldList) {
         return null;
       }