diff --git a/doc/requirements.txt b/doc/requirements.txt
index f9c91a3db..a31eb3896 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -4,7 +4,7 @@
 
 openstackdocstheme>=1.18.1 # Apache-2.0
 sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7' # BSD
-sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4' # BSD
+sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2;python_version>='3.4' # BSD
 reno>=2.5.0 # Apache-2.0
 
 # imported when the source code is parsed for generating documentation: