diff --git a/requirements.txt b/requirements.txt
index 88aa8bc..73f7cc1 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,5 +5,5 @@
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 PyYAML>=3.10 # MIT
 six>=1.10.0 # MIT
-sphinx>=1.6.2 # BSD
+sphinx!=1.6.6,>=1.6.2 # BSD
 openstackdocstheme>=1.17.0 # Apache-2.0