diff --git a/grunt/config/browserify.js b/grunt/config/browserify.js
index 8f2d65e9d..3d6467ffe 100644
--- a/grunt/config/browserify.js
+++ b/grunt/config/browserify.js
@@ -33,7 +33,7 @@ module.exports = {
       ignore: [
         'src/lib/connectors/jquery.js',
         'src/lib/connectors/xhr.js',
-        'when'
+        'bluebird'
       ]
     }
   },
@@ -45,7 +45,7 @@ module.exports = {
       ignore: [
         'src/lib/connectors/angular.js',
         'src/lib/connectors/xhr.js',
-        'when'
+        'bluebird'
       ]
     }
   }
diff --git a/package.json b/package.json
index 35a6fccff..ec1f4835f 100644
--- a/package.json
+++ b/package.json
@@ -69,7 +69,7 @@
     "chalk": "~0.4",
     "forever-agent": "0.5.2",
     "lodash-node": "~2.4",
-    "when": "^3.0.1"
+    "bluebird": "^1.1.1"
   },
   "repository": {
     "type": "git",
diff --git a/src/lib/transport.js b/src/lib/transport.js
index fc874a768..4bfdfb6c6 100644
--- a/src/lib/transport.js
+++ b/src/lib/transport.js
@@ -7,7 +7,7 @@ module.exports = Transport;
 var _ = require('./utils');
 var errors = require('./errors');
 var Host = require('./host');
-var when = require('when');
+var Promise = require('bluebird');
 
 function Transport(config) {
   var self = this;
@@ -96,7 +96,7 @@ Transport.nodesToHostCallbacks = {
 };
 
 Transport.prototype.defer = function () {
-  return when.defer();
+  return Promise.defer();
 };
 
 /**
diff --git a/test/fixtures/keepalive.js b/test/fixtures/keepalive.js
index b7fc94449..0dcea7b48 100644
--- a/test/fixtures/keepalive.js
+++ b/test/fixtures/keepalive.js
@@ -1,6 +1,6 @@
+var clock = require('sinon').useFakeTimers();
 var elasticsearch = require('../../src/elasticsearch');
 var _ = require('lodash-node');
-var clock = require('sinon').useFakeTimers();
 
 var es = elasticsearch.Client({
   host: 'localhost:5555',
@@ -35,4 +35,4 @@ es.search({
   console.log(destroyedSockets);
 });
 
-clock.tick(1);
\ No newline at end of file
+clock.tick(10);
\ No newline at end of file
diff --git a/test/unit/index.js b/test/unit/index.js
index b0f91a4b4..8f437dc25 100644
--- a/test/unit/index.js
+++ b/test/unit/index.js
@@ -1,5 +1,6 @@
-var specDir = __dirname + '/specs';
+require('bluebird').longStackTraces();
 
+var specDir = __dirname + '/specs';
 require('fs').readdirSync(specDir).forEach(function (file) {
   require(specDir + '/' + file);
 });
\ No newline at end of file
diff --git a/test/unit/specs/client_action.js b/test/unit/specs/client_action.js
index 2625dc70e..c97047d09 100644
--- a/test/unit/specs/client_action.js
+++ b/test/unit/specs/client_action.js
@@ -1,7 +1,7 @@
 var ca = require('../../../src/lib/client_action');
 var expect = require('expect.js');
 var _ = require('lodash-node');
-var when = require('when');
+var Promise = require('bluebird');
 
 /**
  * Creates a simple mock of the client, whose "transport" has a request
@@ -18,11 +18,11 @@ function mockClient() {
             cb(void 0, params);
           });
         } else {
-          return when.resolve(params);
+          return Promise.resolve(params);
         }
       },
       defer: function () {
-        return when.defer();
+        return Promise.defer();
       }
     }
   };
diff --git a/test/unit/specs/transport.js b/test/unit/specs/transport.js
index 29bbe6457..fd9c48f1e 100644
--- a/test/unit/specs/transport.js
+++ b/test/unit/specs/transport.js
@@ -1,7 +1,7 @@
 var Transport = require('../../../src/lib/transport');
 var Host = require('../../../src/lib/host');
 var errors = require('../../../src/lib/errors');
-var when = require('when');
+var Promise = require('bluebird');
 
 var sinon = require('sinon');
 var expect = require('expect.js');
@@ -213,7 +213,7 @@ describe('Transport Class', function () {
 
   describe('#defer', function () {
     it('returns a when.js promise by default', function () {
-      expect(Transport.prototype.defer().constructor).to.be(when.defer().constructor);
+      expect(Transport.prototype.defer().constructor).to.be(Promise.defer().constructor);
     });
   });
 
@@ -513,8 +513,9 @@ describe('Transport Class', function () {
         var tran = new Transport();
         shortCircuitRequest(tran);
         var ret = tran.request({});
-        expect(when.isPromise(ret)).to.be(true);
+        expect(Promise.is(ret)).to.be(true);
         expect(ret.abort).to.be.a('function');
+        ret.then(_.noop, _.noop); // prevent complaining from bluebird
       });
       it('promise is always pulled from the defer created by this.defer()', function () {
         var fakePromise = {};
@@ -591,7 +592,9 @@ describe('Transport Class', function () {
         var tran = new Transport({});
         var err;
 
-        tran.request({});
+        var prom = tran.request({});
+        // disregard promise, prevent bluebird's warnings
+        prom.then(_.noop, _.noop);
 
         expect(_.size(clock.timeouts)).to.eql(1);
         _.each(clock.timeouts, function (timer, id) {
@@ -607,7 +610,9 @@ describe('Transport Class', function () {
         });
         var err;
 
-        tran.request({});
+        var prom = tran.request({});
+        // disregard promise, prevent bluebird's warnings
+        prom.then(_.noop, _.noop);
 
         expect(_.size(clock.timeouts)).to.eql(1);
         _.each(clock.timeouts, function (timer, id) {
diff --git a/test/unit/specs/transport_with_server.js b/test/unit/specs/transport_with_server.js
index 2388f699f..ab413350d 100644
--- a/test/unit/specs/transport_with_server.js
+++ b/test/unit/specs/transport_with_server.js
@@ -1,7 +1,6 @@
 var Transport = require('../../../src/lib/transport');
 var Host = require('../../../src/lib/host');
 var errors = require('../../../src/lib/errors');
-var when = require('when');
 var expect = require('expect.js');
 
 var sinon = require('sinon');
@@ -254,7 +253,7 @@ describe('Transport + Mock server', function () {
             good: 'day'
           });
           done();
-        });
+        }, done);
       });
     });