diff --git a/requirements.txt b/requirements.txt
index 39ddcd319..25664f33a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,7 +2,7 @@ oslo.config>=1.2.0
 stevedore>=0.10
 
 # for timeutils
-iso8601>=0.1.4
+iso8601>=0.1.4,!=0.1.5,!=0.1.6
 
 # for jsonutils
 six>=1.4.1