diff --git a/test/parallel/test-async-wrap-disabled-propagate-parent.js b/test/parallel/test-async-wrap-disabled-propagate-parent.js
index 5d5b2b27373690..f0daaeb06d0031 100644
--- a/test/parallel/test-async-wrap-disabled-propagate-parent.js
+++ b/test/parallel/test-async-wrap-disabled-propagate-parent.js
@@ -9,7 +9,6 @@ const providers = Object.keys(async_wrap.Providers);
 const uidSymbol = Symbol('uid');
 
 let cntr = 0;
-let server;
 let client;
 
 function init(uid, type, parentUid, parentHandle) {
@@ -34,7 +33,7 @@ function noop() { }
 async_wrap.setupHooks({ init });
 async_wrap.enable();
 
-server = net.createServer(function(c) {
+const server = net.createServer(function(c) {
   client = c;
   // Allow init callback to run before closing.
   setImmediate(() => {
diff --git a/test/parallel/test-async-wrap-propagate-parent.js b/test/parallel/test-async-wrap-propagate-parent.js
index ad3fdff0165729..34a00c22eeeafd 100644
--- a/test/parallel/test-async-wrap-propagate-parent.js
+++ b/test/parallel/test-async-wrap-propagate-parent.js
@@ -9,7 +9,6 @@ const providers = Object.keys(async_wrap.Providers);
 const uidSymbol = Symbol('uid');
 
 let cntr = 0;
-let server;
 let client;
 
 function init(uid, type, parentUid, parentHandle) {
@@ -34,7 +33,7 @@ function noop() { }
 async_wrap.setupHooks({ init });
 async_wrap.enable();
 
-server = net.createServer(function(c) {
+const server = net.createServer(function(c) {
   client = c;
   // Allow init callback to run before closing.
   setImmediate(() => {
diff --git a/test/parallel/test-stream-writev.js b/test/parallel/test-stream-writev.js
index 2aa992b4a9a785..295bed2959398c 100644
--- a/test/parallel/test-stream-writev.js
+++ b/test/parallel/test-stream-writev.js
@@ -43,25 +43,24 @@ function test(decode, uncork, multi, next) {
     assert(false, 'Should not call _write');
   };
 
-  var expectChunks = decode ?
-    [
-      { encoding: 'buffer',
-        chunk: [104, 101, 108, 108, 111, 44, 32] },
-      { encoding: 'buffer',
-        chunk: [119, 111, 114, 108, 100] },
-      { encoding: 'buffer',
-        chunk: [33] },
-      { encoding: 'buffer',
-        chunk: [10, 97, 110, 100, 32, 116, 104, 101, 110, 46, 46, 46] },
-      { encoding: 'buffer',
-        chunk: [250, 206, 190, 167, 222, 173, 190, 239, 222, 202, 251, 173]}
-    ] : [
-      { encoding: 'ascii', chunk: 'hello, ' },
-      { encoding: 'utf8', chunk: 'world' },
-      { encoding: 'buffer', chunk: [33] },
-      { encoding: 'binary', chunk: '\nand then...' },
-      { encoding: 'hex', chunk: 'facebea7deadbeefdecafbad' }
-    ];
+  var expectChunks = decode ? [
+    { encoding: 'buffer',
+      chunk: [104, 101, 108, 108, 111, 44, 32] },
+    { encoding: 'buffer',
+      chunk: [119, 111, 114, 108, 100] },
+    { encoding: 'buffer',
+      chunk: [33] },
+    { encoding: 'buffer',
+      chunk: [10, 97, 110, 100, 32, 116, 104, 101, 110, 46, 46, 46] },
+    { encoding: 'buffer',
+      chunk: [250, 206, 190, 167, 222, 173, 190, 239, 222, 202, 251, 173]}
+  ] : [
+    { encoding: 'ascii', chunk: 'hello, ' },
+    { encoding: 'utf8', chunk: 'world' },
+    { encoding: 'buffer', chunk: [33] },
+    { encoding: 'binary', chunk: '\nand then...' },
+    { encoding: 'hex', chunk: 'facebea7deadbeefdecafbad' }
+  ];
 
   var actualChunks;
   w._writev = function(chunks, cb) {
diff --git a/test/parallel/test-timers-immediate.js b/test/parallel/test-timers-immediate.js
index 40e91a099815b6..4512ff47fb75a6 100644
--- a/test/parallel/test-timers-immediate.js
+++ b/test/parallel/test-timers-immediate.js
@@ -5,7 +5,6 @@ var assert = require('assert');
 let immediateA = false;
 let immediateB = false;
 let immediateC = [];
-let before;
 
 setImmediate(function() {
   try {
@@ -16,7 +15,7 @@ setImmediate(function() {
   clearImmediate(immediateB);
 });
 
-before = process.hrtime();
+const before = process.hrtime();
 
 immediateB = setImmediate(function() {
   immediateB = true;
diff --git a/test/parallel/test-timers-unref.js b/test/parallel/test-timers-unref.js
index 134b2ffe4c3967..570c51b9ac7a5f 100644
--- a/test/parallel/test-timers-unref.js
+++ b/test/parallel/test-timers-unref.js
@@ -7,7 +7,7 @@ let timeout_fired = false;
 let unref_interval = false;
 let unref_timer = false;
 let unref_callbacks = 0;
-let interval, check_unref, checks = 0;
+let checks = 0;
 
 var LONG_TIME = 10 * 1000;
 var SHORT_TIME = 100;
@@ -28,7 +28,7 @@ setTimeout(function() {
   timeout_fired = true;
 }, LONG_TIME).unref();
 
-interval = setInterval(function() {
+const interval = setInterval(function() {
   unref_interval = true;
   clearInterval(interval);
 }, SHORT_TIME);
@@ -38,7 +38,7 @@ setTimeout(function() {
   unref_timer = true;
 }, SHORT_TIME).unref();
 
-check_unref = setInterval(function() {
+const check_unref = setInterval(function() {
   if (checks > 5 || (unref_interval && unref_timer))
     clearInterval(check_unref);
   checks += 1;