diff --git a/lib/internal/cluster/child.js b/lib/internal/cluster/child.js
index 097c6dafae0172..533174a515bfac 100644
--- a/lib/internal/cluster/child.js
+++ b/lib/internal/cluster/child.js
@@ -128,7 +128,7 @@ function rr(message, indexesKey, cb) {
   if (message.errno)
     return cb(message.errno, null);
 
-  var key = message.key;
+  let key = message.key;
 
   function listen(backlog) {
     // TODO(bnoordhuis) Send a message to the master that tells it to