diff --git a/benchmark/child_process/child-process-exec-stdout.js b/benchmark/child_process/child-process-exec-stdout.js
index a1dc4aa04c72a9..f750e2cf3e68f2 100644
--- a/benchmark/child_process/child-process-exec-stdout.js
+++ b/benchmark/child_process/child-process-exec-stdout.js
@@ -19,7 +19,7 @@ function childProcessExecStdout({ dur, len }) {
   const cmd = `yes "${'.'.repeat(len)}"`;
   const child = exec(cmd, { 'stdio': ['ignore', 'pipe', 'ignore'] });
 
-  var bytes = 0;
+  let bytes = 0;
   child.stdout.on('data', (msg) => {
     bytes += msg.length;
   });
diff --git a/benchmark/child_process/child-process-read-ipc.js b/benchmark/child_process/child-process-read-ipc.js
index a9e9cdf7fd7914..827f75b1e54bd1 100644
--- a/benchmark/child_process/child-process-read-ipc.js
+++ b/benchmark/child_process/child-process-read-ipc.js
@@ -26,7 +26,7 @@ if (process.argv[2] === 'child') {
     const child = spawn(process.argv[0],
                         [process.argv[1], 'child', len], options);
 
-    var bytes = 0;
+    let bytes = 0;
     child.on('message', (msg) => { bytes += msg.length; });
 
     setTimeout(() => {
diff --git a/benchmark/child_process/child-process-read.js b/benchmark/child_process/child-process-read.js
index 3c0144116f589f..01e9846be22b56 100644
--- a/benchmark/child_process/child-process-read.js
+++ b/benchmark/child_process/child-process-read.js
@@ -24,7 +24,7 @@ function main({ dur, len }) {
   const options = { 'stdio': ['ignore', 'pipe', 'ignore'] };
   const child = child_process.spawn('yes', [msg], options);
 
-  var bytes = 0;
+  let bytes = 0;
   child.stdout.on('data', (msg) => {
     bytes += msg.length;
   });