diff --git a/requirements.txt b/requirements.txt
index 3743a4c..94b59ff 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 tornado==4.3
 markdown2 >= 2.1.0
 py-bcrypt >= 0.3
-futures >= 2.1.3
+futures <= 2.2.0, >= 2.1.3
 jsonrpclib==0.1.7
 six==1.10.0