diff --git a/lib/internal/async_hooks.js b/lib/internal/async_hooks.js
index 1e9b89ce5e65ff..ea49239a6178bb 100644
--- a/lib/internal/async_hooks.js
+++ b/lib/internal/async_hooks.js
@@ -262,7 +262,7 @@ function getOrSetAsyncId(object) {
 // the user to safeguard this call and make sure it's zero'd out when the
 // constructor is complete.
 function getDefaultTriggerAsyncId() {
-  var defaultTriggerAsyncId = async_id_fields[kDefaultTriggerAsyncId];
+  let defaultTriggerAsyncId = async_id_fields[kDefaultTriggerAsyncId];
   // If defaultTriggerAsyncId isn't set, use the executionAsyncId
   if (defaultTriggerAsyncId < 0)
     defaultTriggerAsyncId = async_id_fields[kExecutionAsyncId];
@@ -276,7 +276,7 @@ function defaultTriggerAsyncIdScope(triggerAsyncId, block, ...args) {
   const oldDefaultTriggerAsyncId = async_id_fields[kDefaultTriggerAsyncId];
   async_id_fields[kDefaultTriggerAsyncId] = triggerAsyncId;
 
-  var ret;
+  let ret;
   try {
     ret = Reflect.apply(block, null, args);
   } finally {
diff --git a/lib/internal/bootstrap_node.js b/lib/internal/bootstrap_node.js
index 6b718df2acba5a..2766a8d28d0874 100644
--- a/lib/internal/bootstrap_node.js
+++ b/lib/internal/bootstrap_node.js
@@ -173,7 +173,7 @@
           const fs = NativeModule.require('fs');
           // read the source
           const filename = Module._resolveFilename(process.argv[1]);
-          var source = fs.readFileSync(filename, 'utf-8');
+          const source = fs.readFileSync(filename, 'utf-8');
           checkScriptSyntax(source, filename);
           process.exit(0);
         }
@@ -219,7 +219,7 @@
           // Read all of stdin - execute it.
           process.stdin.setEncoding('utf8');
 
-          var code = '';
+          let code = '';
           process.stdin.on('data', function(d) {
             code += d;
           });
@@ -467,7 +467,7 @@
     const versionTypes = icu.getVersion().split(',');
 
     for (var n = 0; n < versionTypes.length; n++) {
-      var name = versionTypes[n];
+      const name = versionTypes[n];
       const version = icu.getVersion(name);
       Object.defineProperty(process.versions, name, {
         writable: false,
@@ -632,7 +632,7 @@
   ];
 
   NativeModule.prototype.compile = function() {
-    var source = NativeModule.getSource(this.id);
+    let source = NativeModule.getSource(this.id);
     source = NativeModule.wrap(source);
 
     this.loading = true;
diff --git a/lib/internal/readline.js b/lib/internal/readline.js
index b15ed4972ef7f2..e3d3007a75c645 100644
--- a/lib/internal/readline.js
+++ b/lib/internal/readline.js
@@ -9,8 +9,8 @@ const ansi =
 
 const kEscape = '\x1b';
 
-var getStringWidth;
-var isFullWidthCodePoint;
+let getStringWidth;
+let isFullWidthCodePoint;
 
 function CSI(strings, ...args) {
   let ret = `${kEscape}[`;