diff --git a/.github/workflows/bench-diff.yml b/.github/workflows/bench-diff.yml
index 6246d30a..df5647cb 100644
--- a/.github/workflows/bench-diff.yml
+++ b/.github/workflows/bench-diff.yml
@@ -18,6 +18,11 @@ jobs:
     permissions:
       checks: write
     steps:
+    - name: Debug event types
+      run: |
+        echo "${{ github.event_name != 'pull_request' && github.sha || github.event.pull_request.head.sha }}"
+        echo "github.sha=${{ github.sha }}"
+        echo "github.event.pull_request.head.sha=${{ github.event.pull_request.head.sha }}"
     - uses: actions/checkout@v4
       with:
         fetch-depth: 0