diff --git a/.github/workflows/python-pull-request.yml b/.github/workflows/python-pull-request.yml
index 337a238..c2be6a4 100644
--- a/.github/workflows/python-pull-request.yml
+++ b/.github/workflows/python-pull-request.yml
@@ -17,7 +17,7 @@ jobs:
   checks:
     strategy:
       matrix:
-        python-version: ["3.10", "3.11", "3.12"]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
     uses: ecmwf-actions/reusable-workflows/.github/workflows/qa-pytest-pyproject.yml@v2
     with:
       python-version: ${{ matrix.python-version }}