diff --git a/doc/requirements.txt b/doc/requirements.txt
index 35a43bf7..f1bac208 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -3,6 +3,6 @@
 # process, which may cause wedges in the gate later.
 
 openstackdocstheme>=1.17.0 # Apache-2.0
-sphinx>=1.6.2 # BSD
+sphinx!=1.6.6,>=1.6.2 # BSD
 reno>=2.5.0 # Apache-2.0
-sphinxcontrib-httpdomain>=1.3.0  # BSD
+sphinxcontrib-httpdomain>=1.3.0 # BSD