diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a06dee37bfa509362f498135f29c1b892ca0cd34..5f8ee422e5677b1c17265e499d503147d159bc55 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -21,7 +21,7 @@ image: python:3.8-alpine
 test:
   stage: test
   script:
-  - pip install -U sphinx
+  - pip3 install -U sphinx sphinx-rtd-theme
   - sphinx-build -b html docs/source/ public/
   - branches
   except: