diff --git a/benchmark/keys.js b/benchmark/keys.js
new file mode 100755
index 0000000..50f8535
--- /dev/null
+++ b/benchmark/keys.js
@@ -0,0 +1,20 @@
+'use strict';
+
+var fileType = require('file-type');
+
+var types = {
+  png: true,
+  jpg: true,
+  tif: true,
+  webp: true
+}
+
+module.exports = function isCwebpReadable(buf) {
+  var type = fileType(buf);
+
+  if (!type) {
+    return false;
+  }
+
+  return !!types[type.ext];
+};
diff --git a/benchmark/runner.js b/benchmark/runner.js
index 0b34707..2651bd7 100755
--- a/benchmark/runner.js
+++ b/benchmark/runner.js
@@ -1,24 +1,29 @@
 /* globals set, suite, bench */
 'use strict';
 
-var main = require('..');
-var indexOf = require('./index-of.js');
-var regex = require('./regex.js');
+const main = require('..');
+const indexOf = require('./index-of.js');
+const keys = require('./keys.js');
+const regex = require('./regex.js');
 
-var fixture = new Buffer(100);
+const fixture = new Buffer(100);
 
-suite('Detect file type', function() {
+suite('Detect file type', () => {
   set('iterations', 30000);
 
-  bench('logical OR (current version)', function() {
+  bench('logical OR (current version)', () => {
     main(fixture);
   });
 
-  bench('array.indexOf', function() {
+  bench('array.indexOf', () => {
     indexOf(fixture);
   });
 
-  bench('regular expression', function() {
+  bench('keys', () => {
+    regex(fixture);
+  });
+
+  bench('regular expression', () => {
     regex(fixture);
   });
 });
diff --git a/package.json b/package.json
index 014cece..2915011 100644
--- a/package.json
+++ b/package.json
@@ -5,7 +5,7 @@
   "repository": "shinnn/is-cwebp-readable",
   "author": "Shinnosuke Watanabe (https://github.com/shinnn)",
   "scripts": {
-    "bench": "matcha benchmark/runner.js",
+    "bench": "node --harmony_arrow_functions node_modules/.bin/_matcha benchmark/runner.js",
     "pretest": "eslint --config node_modules/@shinnn/eslintrc-node/rc.json index.js benchmark test.js",
     "test": "node --harmony_arrow_functions test.js | tap-spec",
     "coverage": "node --harmony_arrow_functions node_modules/.bin/istanbul cover test.js",