diff --git a/doc/requirements.txt b/doc/requirements.txt
index 9e2690a..09871b9 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -3,5 +3,6 @@
 # process, which may cause wedges in the gate later.
 
 openstackdocstheme>=1.18.1 # Apache-2.0
-sphinx>=1.6.2,!=1.6.6,!=1.6.7 # BSD
+sphinx>=1.6.2,!=1.6.6,!=1.6.7,<2.0.0;python_version=='2.7'  # BSD
+sphinx>=1.6.2,!=1.6.6,!=1.6.7;python_version>='3.4' # BSD
 reno>=2.5.0 # Apache-2.0