diff --git a/.github/workflows/test_pr.yml b/.github/workflows/test_pr.yml
index f3dbf84b95..6c753a1cf6 100644
--- a/.github/workflows/test_pr.yml
+++ b/.github/workflows/test_pr.yml
@@ -17,7 +17,7 @@ jobs:
       - name: Run Docker
         run: |
           cd cctbx_project/fable/docker
-          docker buildx build -t fable-dock --build-arg=BUILD_PARENT_DOCKPATH=python:3.9-slim .
+          docker buildx build -t fable-dock --build-arg=BUILD_PARENT_DOCKPATH=debian:sid-slim .
 
       - name: Run example
         run: docker run -i -w $(pwd) --volume=$(pwd):$(pwd):rw -t fable-dock --example