diff --git a/benchmark/buffers/buffer-bytelength.js b/benchmark/buffers/buffer-bytelength.js
index 3246a42d96b34c..1b324a49f89de8 100644
--- a/benchmark/buffers/buffer-bytelength.js
+++ b/benchmark/buffers/buffer-bytelength.js
@@ -16,8 +16,8 @@ const chars = [
 ];
 
 function main({ n, len, encoding }) {
-  var strings = [];
-  var results = [ len * 16 ];
+  let strings = [];
+  let results = [ len * 16 ];
   if (encoding === 'buffer') {
     strings = [ Buffer.alloc(len * 16, 'a') ];
   } else {
diff --git a/benchmark/buffers/buffer-compare-instance-method.js b/benchmark/buffers/buffer-compare-instance-method.js
index 284001c236d99d..eb18fa518037f4 100644
--- a/benchmark/buffers/buffer-compare-instance-method.js
+++ b/benchmark/buffers/buffer-compare-instance-method.js
@@ -12,7 +12,6 @@ function main({ n, size, args }) {
   const b1 = Buffer.alloc(size, 'a');
   const b0Len = b0.length;
   const b1Len = b1.length;
-  var i;
 
   b1[size - 1] = 'b'.charCodeAt(0);
 
@@ -20,7 +19,7 @@ function main({ n, size, args }) {
     case 2:
       b0.compare(b1, 0);
       bench.start();
-      for (i = 0; i < n; i++) {
+      for (let i = 0; i < n; i++) {
         b0.compare(b1, 0);
       }
       bench.end(n);
@@ -28,7 +27,7 @@ function main({ n, size, args }) {
     case 3:
       b0.compare(b1, 0, b1Len);
       bench.start();
-      for (i = 0; i < n; i++) {
+      for (let i = 0; i < n; i++) {
         b0.compare(b1, 0, b1Len);
       }
       bench.end(n);
@@ -36,7 +35,7 @@ function main({ n, size, args }) {
     case 4:
       b0.compare(b1, 0, b1Len, 0);
       bench.start();
-      for (i = 0; i < n; i++) {
+      for (let i = 0; i < n; i++) {
         b0.compare(b1, 0, b1Len, 0);
       }
       bench.end(n);
@@ -44,7 +43,7 @@ function main({ n, size, args }) {
     case 5:
       b0.compare(b1, 0, b1Len, 0, b0Len);
       bench.start();
-      for (i = 0; i < n; i++) {
+      for (let i = 0; i < n; i++) {
         b0.compare(b1, 0, b1Len, 0, b0Len);
       }
       bench.end(n);
@@ -52,7 +51,7 @@ function main({ n, size, args }) {
     default:
       b0.compare(b1);
       bench.start();
-      for (i = 0; i < n; i++) {
+      for (let i = 0; i < n; i++) {
         b0.compare(b1);
       }
       bench.end(n);
diff --git a/benchmark/buffers/buffer-hex.js b/benchmark/buffers/buffer-hex.js
index 1b49ca745381da..33d2b44d6a5950 100644
--- a/benchmark/buffers/buffer-hex.js
+++ b/benchmark/buffers/buffer-hex.js
@@ -9,16 +9,15 @@ const bench = common.createBenchmark(main, {
 
 function main({ len, n }) {
   const buf = Buffer.alloc(len);
-  var i;
 
-  for (i = 0; i < buf.length; i++)
+  for (let i = 0; i < buf.length; i++)
     buf[i] = i & 0xff;
 
   const hex = buf.toString('hex');
 
   bench.start();
 
-  for (i = 0; i < n; i += 1)
+  for (let i = 0; i < n; i += 1)
     Buffer.from(hex, 'hex');
 
   bench.end(n);
diff --git a/benchmark/buffers/buffer-indexof.js b/benchmark/buffers/buffer-indexof.js
index e635da2351c4a7..4c0993a1ef0ef9 100644
--- a/benchmark/buffers/buffer-indexof.js
+++ b/benchmark/buffers/buffer-indexof.js
@@ -25,7 +25,7 @@ const bench = common.createBenchmark(main, {
 });
 
 function main({ n, search, encoding, type }) {
-  var aliceBuffer = fs.readFileSync(
+  let aliceBuffer = fs.readFileSync(
     path.resolve(__dirname, '../fixtures/alice.html')
   );
 
diff --git a/benchmark/buffers/buffer-iterate.js b/benchmark/buffers/buffer-iterate.js
index e81ce2b3035d90..de002108a95d65 100644
--- a/benchmark/buffers/buffer-iterate.js
+++ b/benchmark/buffers/buffer-iterate.js
@@ -29,15 +29,15 @@ function main({ size, type, method, n }) {
 }
 
 function benchFor(buffer, n) {
-  for (var k = 0; k < n; k++) {
-    for (var i = 0; i < buffer.length; i++) {
+  for (let k = 0; k < n; k++) {
+    for (let i = 0; i < buffer.length; i++) {
       assert(buffer[i] === 0);
     }
   }
 }
 
 function benchForOf(buffer, n) {
-  for (var k = 0; k < n; k++) {
+  for (let k = 0; k < n; k++) {
     for (const b of buffer) {
       assert(b === 0);
     }
@@ -45,7 +45,7 @@ function benchForOf(buffer, n) {
 }
 
 function benchIterator(buffer, n) {
-  for (var k = 0; k < n; k++) {
+  for (let k = 0; k < n; k++) {
     const iter = buffer[Symbol.iterator]();
     let cur = iter.next();
 
diff --git a/benchmark/buffers/buffer-swap.js b/benchmark/buffers/buffer-swap.js
index d22bf2fd5504ea..a33bac4ae3ed78 100644
--- a/benchmark/buffers/buffer-swap.js
+++ b/benchmark/buffers/buffer-swap.js
@@ -36,7 +36,7 @@ Buffer.prototype.htons = function htons() {
 Buffer.prototype.htonl = function htonl() {
   if (this.length % 4 !== 0)
     throw new RangeError();
-  for (var i = 0; i < this.length; i += 4) {
+  for (let i = 0; i < this.length; i += 4) {
     swap(this, i, i + 3);
     swap(this, i + 1, i + 2);
   }
@@ -66,7 +66,7 @@ function createBuffer(len, aligned) {
 function genMethod(method) {
   const fnString = `
       return function ${method}(n, buf) {
-        for (var i = 0; i <= n; i++)
+        for (let i = 0; i <= n; i++)
           buf.${method}();
       }`;
   return (new Function(fnString))();
diff --git a/benchmark/buffers/buffer-tostring.js b/benchmark/buffers/buffer-tostring.js
index 88543d8fd3af5a..98d6ab3fa08311 100644
--- a/benchmark/buffers/buffer-tostring.js
+++ b/benchmark/buffers/buffer-tostring.js
@@ -15,29 +15,28 @@ function main({ encoding, args, len, n }) {
   if (encoding.length === 0)
     encoding = undefined;
 
-  var i;
   switch (args) {
     case 1:
       bench.start();
-      for (i = 0; i < n; i += 1)
+      for (let i = 0; i < n; i += 1)
         buf.toString(encoding);
       bench.end(n);
       break;
     case 2:
       bench.start();
-      for (i = 0; i < n; i += 1)
+      for (let i = 0; i < n; i += 1)
         buf.toString(encoding, 0);
       bench.end(n);
       break;
     case 3:
       bench.start();
-      for (i = 0; i < n; i += 1)
+      for (let i = 0; i < n; i += 1)
         buf.toString(encoding, 0, len);
       bench.end(n);
       break;
     default:
       bench.start();
-      for (i = 0; i < n; i += 1)
+      for (let i = 0; i < n; i += 1)
         buf.toString();
       bench.end(n);
       break;
diff --git a/benchmark/buffers/buffer-write-string.js b/benchmark/buffers/buffer-write-string.js
index b30edcf8867adf..cd24d379728cda 100644
--- a/benchmark/buffers/buffer-write-string.js
+++ b/benchmark/buffers/buffer-write-string.js
@@ -15,21 +15,19 @@ function main({ len, n, encoding, args }) {
   let start = 0;
   const buf = Buffer.allocUnsafe(len);
 
-  var i;
-
   switch (args) {
     case 'offset':
       string = 'a'.repeat(Math.floor(len / 2));
       start = len - string.length;
       if (encoding) {
         bench.start();
-        for (i = 0; i < n; ++i) {
+        for (let i = 0; i < n; ++i) {
           buf.write(string, start, encoding);
         }
         bench.end(n);
       } else {
         bench.start();
-        for (i = 0; i < n; ++i) {
+        for (let i = 0; i < n; ++i) {
           buf.write(string, start);
         }
         bench.end(n);
@@ -39,13 +37,13 @@ function main({ len, n, encoding, args }) {
       string = 'a'.repeat(len);
       if (encoding) {
         bench.start();
-        for (i = 0; i < n; ++i) {
+        for (let i = 0; i < n; ++i) {
           buf.write(string, 0, buf.length, encoding);
         }
         bench.end(n);
       } else {
         bench.start();
-        for (i = 0; i < n; ++i) {
+        for (let i = 0; i < n; ++i) {
           buf.write(string, 0, buf.length);
         }
         bench.end(n);
@@ -55,13 +53,13 @@ function main({ len, n, encoding, args }) {
       string = 'a'.repeat(len);
       if (encoding) {
         bench.start();
-        for (i = 0; i < n; ++i) {
+        for (let i = 0; i < n; ++i) {
           buf.write(string, encoding);
         }
         bench.end(n);
       } else {
         bench.start();
-        for (i = 0; i < n; ++i) {
+        for (let i = 0; i < n; ++i) {
           buf.write(string);
         }
         bench.end(n);