diff --git a/doc/requirements.txt b/doc/requirements.txt
index e1583c25a..5335029d7 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -3,4 +3,4 @@
 # process, which may cause wedges in the gate later.
 oslo.config>=5.1.0 # Apache-2.0
 openstackdocstheme>=1.17.0 # Apache-2.0
-sphinx>=1.6.2 # BSD
+sphinx!=1.6.6,>=1.6.2 # BSD