diff --git a/doc/requirements.txt b/doc/requirements.txt
index 9b5e73810..ffd53839a 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -4,6 +4,6 @@
 oslo.config>=5.2.0 # Apache-2.0
 openstackdocstheme>=1.24.0 # 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>=2.7.0 # Apache-2.0
 docutils>=0.11  # OSI-Approved Open Source, Public Domain