diff --git a/lib/domain.js b/lib/domain.js
index b980f8452c2113..3a5d7614c4f4cb 100644
--- a/lib/domain.js
+++ b/lib/domain.js
@@ -204,7 +204,7 @@ Domain.prototype.members = undefined;
 
 // Called by process._fatalException in case an error was thrown.
 Domain.prototype._errorHandler = function(er) {
-  var caught = false;
+  let caught = false;
 
   if ((typeof er === 'object' && er !== null) || typeof er === 'function') {
     Object.defineProperty(er, 'domain', {
@@ -324,7 +324,7 @@ Domain.prototype.add = function(ee) {
   // e.add(d);
   // e.emit('error', er); // RangeError, stack overflow!
   if (this.domain && (ee instanceof Domain)) {
-    for (var d = this.domain; d; d = d.domain) {
+    for (let d = this.domain; d; d = d.domain) {
       if (ee === d) return;
     }
   }
@@ -348,14 +348,14 @@ Domain.prototype.remove = function(ee) {
 
 
 Domain.prototype.run = function(fn) {
-  var ret;
+  let ret;
 
   this.enter();
   if (arguments.length >= 2) {
-    var len = arguments.length;
-    var args = new Array(len - 1);
+    const len = arguments.length;
+    const args = new Array(len - 1);
 
-    for (var i = 1; i < len; i++)
+    for (let i = 1; i < len; i++)
       args[i - 1] = arguments[i];
 
     ret = fn.apply(this, args);
@@ -370,7 +370,7 @@ Domain.prototype.run = function(fn) {
 
 function intercepted(_this, self, cb, fnargs) {
   if (fnargs[0] && fnargs[0] instanceof Error) {
-    var er = fnargs[0];
+    const er = fnargs[0];
     er.domainBound = cb;
     er.domainThrown = false;
     Object.defineProperty(er, 'domain', {
@@ -384,11 +384,11 @@ function intercepted(_this, self, cb, fnargs) {
   }
 
   const args = [];
-  var i, ret;
+  let ret;
 
   self.enter();
   if (fnargs.length > 1) {
-    for (i = 1; i < fnargs.length; i++)
+    for (let i = 1; i < fnargs.length; i++)
       args.push(fnargs[i]);
     ret = cb.apply(_this, args);
   } else {
@@ -412,7 +412,7 @@ Domain.prototype.intercept = function(cb) {
 
 
 function bound(_this, self, cb, fnargs) {
-  var ret;
+  let ret;
 
   self.enter();
   if (fnargs.length > 0)