diff --git a/lib/cluster.js b/lib/cluster.js
index 68a772a74a9b59..cf066657954bf8 100644
--- a/lib/cluster.js
+++ b/lib/cluster.js
@@ -244,8 +244,8 @@ function masterInit() {
       execArgv: process.execArgv,
       silent: false
     };
-    settings = util._extend(settings, cluster.settings);
-    settings = util._extend(settings, options || {});
+    settings = Object.assign(settings, cluster.settings);
+    settings = Object.assign(settings, options || {});
     // Tell V8 to write profile data for each process to a separate file.
     // Without --logfile=v8-%p.log, everything ends up in a single, unusable
     // file. (Unusable because what V8 logs are memory addresses and each
@@ -297,10 +297,10 @@ function masterInit() {
   var debugPortOffset = 1;
 
   function createWorkerProcess(id, env) {
-    var workerEnv = util._extend({}, process.env);
+    var workerEnv = Object.assign({}, process.env);
     var execArgv = cluster.settings.execArgv.slice();
 
-    workerEnv = util._extend(workerEnv, env);
+    workerEnv = Object.assign(workerEnv, env);
     workerEnv.NODE_UNIQUE_ID = '' + id;
 
     for (var i = 0; i < execArgv.length; i++) {
@@ -495,7 +495,7 @@ function masterInit() {
 
     // Set custom server data
     handle.add(worker, function(errno, reply, handle) {
-      reply = util._extend({
+      reply = Object.assign({
         errno: errno,
         key: key,
         ack: message.seq,
@@ -573,7 +573,7 @@ function workerInit() {
     else
       indexes[key]++;
 
-    const message = util._extend({
+    const message = Object.assign({
       act: 'queryServer',
       index: indexes[key],
       data: null
@@ -640,7 +640,7 @@ function workerInit() {
     }
 
     function getsockname(out) {
-      if (key) util._extend(out, message.sockname);
+      if (key) Object.assign(out, message.sockname);
       return 0;
     }
 
@@ -735,7 +735,7 @@ var seq = 0;
 var callbacks = {};
 function sendHelper(proc, message, handle, cb) {
   // Mark message as internal. See INTERNAL_PREFIX in lib/child_process.js
-  message = util._extend({ cmd: 'NODE_CLUSTER' }, message);
+  message = Object.assign({ cmd: 'NODE_CLUSTER' }, message);
   if (cb) callbacks[seq] = cb;
   message.seq = seq;
   seq += 1;