diff --git a/setup.py b/setup.py
index 7d49a89b..208ce81d 100644
--- a/setup.py
+++ b/setup.py
@@ -51,7 +51,8 @@
         'pytest>=2.7.3',
         'gevent==1.1rc1',
         'six>=1.10.0',
-        'pytest-mock'
+        'pytest-mock',
+        'promise>=0.4.2'
     ],
     extras_require={
         'gevent': [