diff --git a/doc/requirements.txt b/doc/requirements.txt
index afd3597..66a11d0 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,4 +1,5 @@
-sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
+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,!=2.1.0,>=1.6.2;python_version>='3.4' # BSD
 openstackdocstheme>=1.18.1  # Apache-2.0
 # releasenotes
 reno>=2.5.0 # Apache-2.0