diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 3a742db..554e591 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -50,7 +50,11 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: bec/csaxs_bec
-          ref: "${{ inputs.BEC_PLUGIN_REPO_BRANCH || github.head_ref || github.sha }}"
+          # For pull_request events github.sha is the test-merge commit, which
+          # lives in the base repo, so this works for fork PRs too. Using
+          # github.head_ref here would try to fetch the fork's branch name from
+          # bec/csaxs_bec, where it does not exist -> checkout fails (exit 1).
+          ref: "${{ inputs.BEC_PLUGIN_REPO_BRANCH || github.sha }}"
           path: ./csaxs_bec
 
       - name: Lint for merge conflicts from template updates