diff --git a/lib/workers/worker-browser.js b/lib/workers/worker-browser.js
index 58386bbc..b53af601 100644
--- a/lib/workers/worker-browser.js
+++ b/lib/workers/worker-browser.js
@@ -7,7 +7,7 @@
 
 'use strict';
 
-let Master = require('./master');
+const Master = require('./master');
 
 self.onmessage = function onmessage(event) {
   let env, server;
diff --git a/lib/workers/worker.js b/lib/workers/worker.js
index 1d1d25f9..bce8c991 100644
--- a/lib/workers/worker.js
+++ b/lib/workers/worker.js
@@ -7,7 +7,7 @@
 
 'use strict';
 
-let Master = require('./master');
-let server = new Master();
+const Master = require('./master');
+const server = new Master();
 
 server.listen(process.env);