diff --git a/.github/workflows/manual_tests.yml b/.github/workflows/manual_tests.yml
index 2781c64..8c5455b 100644
--- a/.github/workflows/manual_tests.yml
+++ b/.github/workflows/manual_tests.yml
@@ -63,11 +63,9 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install pdm
-        run: pip install pdm
+        run: pip install pdm "fiona==1.9.6"
       - name: Generate lock with oldest dependencies
-        run: |
-          pdm add "fiona<1.10"
-          pdm lock --lockfile pdm.oldest.lock --strategy no_cross_platform,direct_minimal_versions -G cli -dG test
+        run: pdm lock --lockfile pdm.oldest.lock --strategy no_cross_platform,direct_minimal_versions -G cli -dG test
       - name: Install quackosm and tests dependencies
         run: pdm install --lockfile pdm.oldest.lock -G cli -dG test --skip=post_install
       - name: Run tests with pytest