diff --git a/docs/requirements.txt b/docs/requirements.txt
index 755bb966..5896d270 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -4,3 +4,4 @@ sphinx-copybutton==0.2.11
 pathlib
 git+https://github.com/fabpot/sphinx-php.git
 jinja2<3.1.0
+alabaster<0.7.14