diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 4f1e6568b9317752214ac8654b38990752eec9e7..e0331f1b3a86f533ba2cfec432a1a7a58627b102 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -71,7 +71,7 @@ Python 3 POCL:
 
 Documentation:
   script:
-  - EXTRA_INSTALL="pybind11 numpy"
+  - EXTRA_INSTALL="pybind11 cython numpy"
   - curl -L -O -k https://gitlab.tiker.net/inducer/ci-support/raw/master/build-docs.sh
   - ". ./build-docs.sh"
   tags: