diff --git a/lib/index.js b/lib/index.js
index 7e8aed6..820d90d 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -16,7 +16,8 @@ var oneDay = 86400 * 1000;
 
 var inherits = require('util').inherits,
 	events = require('events'),
-	MongoClient = require('mongodb').MongoClient;
+	MongoClient = require('mongodb').MongoClient,
+	Db = require('mongodb').Db;
 
 var createIndexes = function(collection, callback) {
 	var times = 2;
@@ -31,7 +32,7 @@ var createIndexes = function(collection, callback) {
 };
 
 var makeConnectionString = function(options) {
-	return  'mongodb://' + (options.host || '127.0.0.1') + ':' +
+	return 'mongodb://' + (options.host || '127.0.0.1') + ':' +
 		(options.port || '27017') + '/' +
 		(options.db || 'test') +
 		'?ssl=' + (options.ssl || false);
@@ -47,17 +48,17 @@ var makeConnectionString = function(options) {
 module.exports = function(connect) {
 
 	/**
-	* Connect's Store.
-	*/
+	 * Connect's Store.
+	 */
 
 	var Store = connect.Store || connect.session.Store;
 
 	/**
-	* Initialize MongoStore with the given `options`.
-	*
-	* @param {Object} options
-	* @api public
-	*/
+	 * Initialize MongoStore with the given `options`.
+	 *
+	 * @param {Object} options
+	 * @api public
+	 */
 
 	function MongoStore(options) {
 		var self = this;
@@ -76,10 +77,37 @@ module.exports = function(connect) {
 			createIndexes(this.col, emitConnect);
 		} else {
 			var dbUrl = options.url || makeConnectionString(options);
-			MongoClient.connect(dbUrl, function(err, db) {
+			var opts = {};
+			if (options.user && options.password) {
+				opts.auth = {
+					user: options.user,
+					password: options.password
+				};
+			}
+			MongoClient.connect(dbUrl, opts, function(err, client) {
 				if (err) throw err;
+				var db;
+				if (client instanceof MongoClient) {
+					var dbName = 'test';
+					if (typeof options.db === 'string') {
+						dbName === options.db;
+					} else if (
+						client.s && client.s.options &&
+						typeof client.s.options.dbName === 'string'
+					) {
+						dbName = client.s.options.dbName;
+					}
+					db = client.db(dbName);
+				} else if (client instanceof Db) {
+					db = client;
+				} else {
+					throw new Error('mongodb connect failed');
+				}
 				self.col = db.collection(options.collection || 'sessions');
-				if (options.user && options.password) {
+				if (
+					options.user && options.password &&
+					typeof db.authenticate === 'function'
+				) {
 					db.authenticate(options.user, options.password, function(err, res) {
 						if (err) throw err;
 						if (!res) throw new Error('mongodb authentication failed');
@@ -93,62 +121,65 @@ module.exports = function(connect) {
 	};
 
 	/**
-	* Inherit from `Store`.
-	*/
+	 * Inherit from `Store`.
+	 */
 
 	inherits(MongoStore, Store);
 
 	/**
-	* Attempt to fetch session by the given `sid`.
-	*
-	* @param {String} sid
-	* @param {Function} fn
-	* @api public
-	*/
-
-	MongoStore.prototype.get = function(sid, fn){
-		this.col.findOne({sid: sid}, {_id: 0, ttl: 0, sid: 0}, function(err, data) {
-			if (err) return fn(err);
-			if (!data) return fn();
-			return fn(null, data);
-		});
+	 * Attempt to fetch session by the given `sid`.
+	 *
+	 * @param {String} sid
+	 * @param {Function} fn
+	 * @api public
+	 */
+
+	MongoStore.prototype.get = function(sid, fn) {
+		this.col.findOne({sid: sid}, {projection: {_id: 0, ttl: 0, sid: 0}})
+			.then(function(data) {
+				if (!data) return fn();
+				return fn(null, data);
+			})
+			.catch(fn);
 	};
 
 	/**
-	* Commit the given `sess` object associated with the given `sid`.
-	*
-	* @param {String} sid
-	* @param {Session} sess
-	* @param {Function} fn
-	* @api public
-	*/
+	 * Commit the given `sess` object associated with the given `sid`.
+	 *
+	 * @param {String} sid
+	 * @param {Session} sess
+	 * @param {Function} fn
+	 * @api public
+	 */
 
 	MongoStore.prototype.set = function(sid, sess, fn) {
-		try {
-			var maxAge = sess.cookie.maxAge;
+		var maxAge = sess.cookie.maxAge;
 
-			sess.sid = sid;
-			sess.ttl = new Date((this.ttl || ('number' === typeof maxAge
-				? maxAge : oneDay)) + Date.now());
+		sess.sid = sid;
+		sess.ttl = new Date((this.ttl || ('number' === typeof maxAge
+			? maxAge : oneDay)) + Date.now());
 
-			this.col.replaceOne({sid: sid}, sess, {upsert: true}, function() {
-				fn && fn.apply(this, arguments);
-			});
-		} catch (err) {
-			fn && fn(err);
-		}
+		this.col.replaceOne({sid: sid}, sess, {upsert: true})
+			.then(function() {
+				fn(null, true);
+			})
+			.catch(fn);
 	};
 
 	/**
-	* Destroy the session associated with the given `sid`.
-	*
-	* @param {String} sid
-	* @param {Function} fn
-	* @api public
-	*/
+	 * Destroy the session associated with the given `sid`.
+	 *
+	 * @param {String} sid
+	 * @param {Function} fn
+	 * @api public
+	 */
 
 	MongoStore.prototype.destroy = function(sid, fn) {
-		this.col.deleteOne({sid: sid}, fn);
+		this.col.deleteOne({sid: sid})
+			.then(function() {
+				fn();
+			})
+			.catch(fn);
 	};
 
 	return MongoStore;
diff --git a/test.js b/test.js
index 7acdc01..8c84b17 100644
--- a/test.js
+++ b/test.js
@@ -9,9 +9,9 @@ var assert = require('assert'),
 
 var testsCount = 3;
 
-var done = (function () {
+var done = (function() {
 	var count = 0;
-	return function () {
+	return function() {
 		++count;
 		if (count == testsCount) {
 			console.log('done');
@@ -28,19 +28,21 @@ store.on('connect', function() {
 });
 
 // test with initialized db object
-MongoClient.connect('mongodb://127.0.0.1:27017/testdb', function(err, db) {
-	var store = new MongoStore({db: db});
+MongoClient.connect('mongodb://127.0.0.1:27017/testdb', function(err, client) {
+	var db = client instanceof MongoClient ? client.db('testdb') : client;
+	var store = new MongoStore({ db: db });
 	store.on('connect', function() {
 		baseTest.apply(this);
 	});
 });
 
 // test mongodb auth
-MongoClient.connect('mongodb://127.0.0.1:27017/testauth', function(err, db) {
+MongoClient.connect('mongodb://127.0.0.1:27017/testauth', function(err, client) {
+	var db = client instanceof MongoClient ? client.db('testauth') : client;
 	db.removeUser('user', function() {
-		db.addUser('user', 'pass', {roles: ['readWrite']}, function(err, res) {
+		db.addUser('user', 'pass', { roles: ['readWrite'] }, function(err, res) {
 			assert.ok(!err, '#addUser error');
-			var store = new MongoStore({user: 'user', password: 'pass', db: 'testauth'});
+			var store = new MongoStore({ user: 'user', password: 'pass', db: 'testauth' });
 			store.on('connect', function() {
 				baseTest.apply(this);
 			});
@@ -52,7 +54,7 @@ MongoClient.connect('mongodb://127.0.0.1:27017/testauth', function(err, db) {
 function baseTest() {
 	var self = this;
 	// #set()
-	self.set('123', {cookie: {maxAge: 2000}, name: 'name'}, function(err, ok) {
+	self.set('123', { cookie: { maxAge: 2000 }, name: 'name' }, function(err, ok) {
 		assert.ok(!err, '#set() got an error');
 		assert.ok(ok, '#set() is not ok');
 
@@ -60,12 +62,12 @@ function baseTest() {
 		self.get('123', function(err, data) {
 			assert.ok(!err, '#get() got an error');
 			assert.deepEqual({
-				cookie: {maxAge: 2000},
+				cookie: { maxAge: 2000 },
 				name: 'name'
 			}, data);
 
 			// #set null
-			self.set('123', {cookie: {maxAge: 2000}, name: 'name'}, function() {
+			self.set('123', { cookie: { maxAge: 2000 }, name: 'name' }, function() {
 				self.destroy('123', function() {
 					done();
 				});