diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index cc7eca5384bede4499de5dd783317f23d0476ceb..2bca2afa1ca3f309328f4dc377a417903c58f5b3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -129,8 +129,10 @@ unittest_py39:
   image: $CI_REGISTRY_IMAGE
   needs: [build-testenv]
   script:
-      - python3 -c "import caosdb; print('CaosDB Version:', caosdb.__version__)"
-      - tox
+    # First verify that system Python actually is 3.9
+    - python -c "import sys; assert sys.version.startswith('3.9')"
+    - python3 -c "import caosdb; print('CaosDB Version:', caosdb.__version__)"
+    - tox
 
 unittest_py38:
   tags: [docker]