diff --git a/requirements.txt b/requirements.txt
index 5fe951b7..b4cfe231 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,7 +2,8 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 pbr>=2.0.0
-sphinx!=1.6.1,>=1.5.1
+sphinx>=1.5.1,!=1.6.6,!=1.6.7,<2.0.0;python_version=='2.7'  # BSD
+sphinx>=1.5.1,!=1.6.6,!=1.6.7,!=2.1.0;python_version>='3.4'  # BSD
 sphinxcontrib-blockdiag
 openstackdocstheme>=1.17.0 # Apache-2.0
 stestr>=2.0.0 # Apache-2.0