diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index da7f731b87b9d0caf2754aa1c2b849c34aeaa11e..2c0b01bb0177481e4c8c0c65cb69915ca633a5b2 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -78,6 +78,7 @@ pages:
     image: python:3.7-alpine
     script:
       - pip install -U sphinx
+      - pip install sphinx_rtd_theme
       - sphinx-build -b html docs public
     artifacts:
       paths: