diff --git a/doc/requirements.txt b/doc/requirements.txt
index 7a54e0a7780..b9767c37adc 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -4,7 +4,8 @@
 openstackdocstheme>=1.18.1 # Apache-2.0
 reno>=2.5.0 # Apache-2.0
 doc8>=0.6.0 # Apache-2.0
-sphinx!=1.6.6,>=1.6.2 # BSD
+sphinx>=1.6.2,!=1.6.6,<2.0.0;python_version=='2.7' # BSD
+sphinx>=1.6.2,!=1.6.6;python_version>='3.4' # BSD
 mock>=2.0.0 # BSD
 os-api-ref>=1.4.0 # Apache-2.0
 ddt>=1.0.1 # MIT