diff --git a/.gitattributes b/.gitattributes
index 391f0a4..6313b56 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,2 +1 @@
-* text=auto
-*.js text eol=lf
+* text=auto eol=lf
diff --git a/.travis.yml b/.travis.yml
index 7d69d74..2ae9d62 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,5 @@
 language: node_js
 node_js:
+  - '10'
   - '8'
   - '6'
-  - '4'
diff --git a/index.js b/index.js
index 42dc788..5c29152 100644
--- a/index.js
+++ b/index.js
@@ -4,47 +4,54 @@ const isPromise = require('p-is-promise');
 
 const cacheStore = new WeakMap();
 
-const defaultCacheKey = function (x) {
-	if (arguments.length === 1 && (x === null || x === undefined || (typeof x !== 'function' && typeof x !== 'object'))) {
-		return x;
+const defaultCacheKey = (...args) => {
+	if (args.length === 1) {
+		const [firstArgument] = args;
+		if (
+			firstArgument === null ||
+			firstArgument === undefined ||
+			(typeof firstArgument !== 'function' && typeof firstArgument !== 'object')
+		) {
+			return firstArgument;
+		}
 	}
 
-	return JSON.stringify(arguments);
+	return JSON.stringify(args);
 };
 
-module.exports = (fn, opts) => {
-	opts = Object.assign({
+module.exports = (fn, options) => {
+	options = Object.assign({
 		cacheKey: defaultCacheKey,
 		cache: new Map(),
 		cachePromiseRejection: false
-	}, opts);
+	}, options);
 
-	const memoized = function () {
+	const memoized = function (...args) {
 		const cache = cacheStore.get(memoized);
-		const key = opts.cacheKey.apply(null, arguments);
+		const key = options.cacheKey(...args);
 
 		if (cache.has(key)) {
 			const c = cache.get(key);
 
-			if (typeof opts.maxAge !== 'number' || Date.now() < c.maxAge) {
+			if (typeof options.maxAge !== 'number' || Date.now() < c.maxAge) {
 				return c.data;
 			}
 
 			cache.delete(key);
 		}
 
-		const ret = fn.apply(this, arguments);
+		const ret = fn.call(this, ...args);
 
 		const setData = (key, data) => {
 			cache.set(key, {
 				data,
-				maxAge: Date.now() + (opts.maxAge || 0)
+				maxAge: Date.now() + (options.maxAge || 0)
 			});
 		};
 
 		setData(key, ret);
 
-		if (isPromise(ret) && opts.cachePromiseRejection === false) {
+		if (isPromise(ret) && options.cachePromiseRejection === false) {
 			// Remove rejected promises from cache unless `cachePromiseRejection` is set to `true`
 			ret.catch(() => cache.delete(key));
 		}
@@ -54,7 +61,7 @@ module.exports = (fn, opts) => {
 
 	mimicFn(memoized, fn);
 
-	cacheStore.set(memoized, opts.cache);
+	cacheStore.set(memoized, options.cache);
 
 	return memoized;
 };
diff --git a/package.json b/package.json
index bee8462..0ace1d7 100644
--- a/package.json
+++ b/package.json
@@ -1,43 +1,43 @@
 {
-  "name": "mem",
-  "version": "3.0.1",
-  "description": "Memoize functions - An optimization used to speed up consecutive function calls by caching the result of calls with identical input",
-  "license": "MIT",
-  "repository": "sindresorhus/mem",
-  "author": {
-    "name": "Sindre Sorhus",
-    "email": "sindresorhus@gmail.com",
-    "url": "sindresorhus.com"
-  },
-  "engines": {
-    "node": ">=4"
-  },
-  "scripts": {
-    "test": "xo && ava"
-  },
-  "files": [
-    "index.js"
-  ],
-  "keywords": [
-    "memoize",
-    "function",
-    "mem",
-    "memoization",
-    "cache",
-    "caching",
-    "optimize",
-    "performance",
-    "ttl",
-    "expire",
-    "promise"
-  ],
-  "dependencies": {
-    "mimic-fn": "^1.0.0",
-    "p-is-promise": "^1.1.0"
-  },
-  "devDependencies": {
-    "ava": "*",
-    "delay": "^2.0.0",
-    "xo": "*"
-  }
+	"name": "mem",
+	"version": "3.0.1",
+	"description": "Memoize functions - An optimization used to speed up consecutive function calls by caching the result of calls with identical input",
+	"license": "MIT",
+	"repository": "sindresorhus/mem",
+	"author": {
+		"name": "Sindre Sorhus",
+		"email": "sindresorhus@gmail.com",
+		"url": "sindresorhus.com"
+	},
+	"engines": {
+		"node": ">=6"
+	},
+	"scripts": {
+		"test": "xo && ava"
+	},
+	"files": [
+		"index.js"
+	],
+	"keywords": [
+		"memoize",
+		"function",
+		"mem",
+		"memoization",
+		"cache",
+		"caching",
+		"optimize",
+		"performance",
+		"ttl",
+		"expire",
+		"promise"
+	],
+	"dependencies": {
+		"mimic-fn": "^1.0.0",
+		"p-is-promise": "^1.1.0"
+	},
+	"devDependencies": {
+		"ava": "*",
+		"delay": "^3.0.0",
+		"xo": "*"
+	}
 }
diff --git a/readme.md b/readme.md
index ee9d89e..72575a7 100644
--- a/readme.md
+++ b/readme.md
@@ -40,35 +40,37 @@ memoized('bar');
 const mem = require('mem');
 
 let i = 0;
-const counter = () => Promise.resolve(++i);
+const counter = async () => ++i;
 const memoized = mem(counter);
 
-memoized().then(a => {
-	console.log(a);
+(async () => {
+	console.log(await memoized());
 	//=> 1
 
-	memoized().then(b => {
-		// The return value didn't increase as it's cached
-		console.log(b);
-		//=> 1
-	});
-});
+	// The return value didn't increase as it's cached
+	console.log(await memoized());
+	//=> 1
+})();
 ```
 
 ```js
 const mem = require('mem');
 const got = require('got');
+const delay = require('delay');
+
 const memGot = mem(got, {maxAge: 1000});
 
-memGot('sindresorhus.com').then(() => {
+(async () => {
+	await memGot('sindresorhus.com');
+
 	// This call is cached
-	memGot('sindresorhus.com').then(() => {
-		setTimeout(() => {
-			// This call is not cached as the cache has expired
-			memGot('sindresorhus.com').then(() => {});
-		}, 2000);
-	});
-});
+	await memGot('sindresorhus.com');
+
+	await delay(2000);
+
+	// This call is not cached as the cache has expired
+	await memGot('sindresorhus.com');
+})();
 ```
 
 
@@ -84,6 +86,8 @@ Function to be memoized.
 
 #### options
 
+Type: `Object`
+
 ##### maxAge
 
 Type: `number`<br>
@@ -140,12 +144,14 @@ const got = require('got');
 const cache = new StatsMap();
 const memGot = mem(got, {cache});
 
-memGot('sindresorhus.com')
-	.then(() => memGot('sindresorhus.com'))
-	.then(() => memGot('sindresorhus.com'));
+(async () => {
+	await memGot('sindresorhus.com');
+	await memGot('sindresorhus.com');
+	await memGot('sindresorhus.com');
 
-console.log(cache.stats);
-//=> {hits: 2, misses: 1}
+	console.log(cache.stats);
+	//=> {hits: 2, misses: 1}
+})();
 ```