diff --git a/test/parallel/test-os.js b/test/parallel/test-os.js
index f7fe4634c40dca..15fd189f9be20e 100644
--- a/test/parallel/test-os.js
+++ b/test/parallel/test-os.js
@@ -13,7 +13,7 @@ if (common.isWindows) {
   process.env.TEMP = '';
   assert.equal(os.tmpdir(), '/tmp');
   process.env.TMP = '';
-  var expected = (process.env.SystemRoot || process.env.windir) + '\\temp';
+  const expected = (process.env.SystemRoot || process.env.windir) + '\\temp';
   assert.equal(os.tmpdir(), expected);
   process.env.TEMP = '\\temp\\';
   assert.equal(os.tmpdir(), '\\temp');
@@ -83,21 +83,25 @@ var interfaces = os.networkInterfaces();
 console.error(interfaces);
 switch (platform) {
   case 'linux':
-    var filter = function(e) { return e.address == '127.0.0.1'; };
-    var actual = interfaces.lo.filter(filter);
-    var expected = [{ address: '127.0.0.1', netmask: '255.0.0.0',
-                      mac: '00:00:00:00:00:00', family: 'IPv4',
-                      internal: true }];
-    assert.deepEqual(actual, expected);
-    break;
+    {
+      const filter = function(e) { return e.address == '127.0.0.1'; };
+      const actual = interfaces.lo.filter(filter);
+      const expected = [{ address: '127.0.0.1', netmask: '255.0.0.0',
+                        mac: '00:00:00:00:00:00', family: 'IPv4',
+                        internal: true }];
+      assert.deepEqual(actual, expected);
+      break;
+    }
   case 'win32':
-    var filter = function(e) { return e.address == '127.0.0.1'; };
-    var actual = interfaces['Loopback Pseudo-Interface 1'].filter(filter);
-    var expected = [{ address: '127.0.0.1', netmask: '255.0.0.0',
-                      mac: '00:00:00:00:00:00', family: 'IPv4',
-                      internal: true }];
-    assert.deepEqual(actual, expected);
-    break;
+    {
+      const filter = function(e) { return e.address == '127.0.0.1'; };
+      const actual = interfaces['Loopback Pseudo-Interface 1'].filter(filter);
+      const expected = [{ address: '127.0.0.1', netmask: '255.0.0.0',
+                        mac: '00:00:00:00:00:00', family: 'IPv4',
+                        internal: true }];
+      assert.deepEqual(actual, expected);
+      break;
+    }
 }
 
 var EOL = os.EOL;