diff --git a/doc/requirements.txt b/doc/requirements.txt
index cd8def52e..25c050858 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -3,7 +3,7 @@
 # process, which may cause wedges in the gate later.
 # this is required for the docs build jobs
 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
 sphinxcontrib-apidoc>=0.2.0 # BSD
 openstackdocstheme>=1.11.0 # Apache-2.0
 reno>=1.8.0  # Apache-2.0