diff --git a/doc/requirements.txt b/doc/requirements.txt
index 77d1fe88bf..16c92c31ed 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,3 +1,4 @@
+mock>=2.0.0 # BSD
 openstackdocstheme>=1.18.1 # Apache-2.0
 os-api-ref>=1.4.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0