diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index a7d6e3e6c..5dedd579c 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -42,7 +42,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2.3.4
       with:
-        ref: ${{ github.event.pull_request.head.ref }}
+        ref: refs/pr/${{ github.event.number }}/merge
         repository: ${{ github.event.pull_request.head.repo.full_name }}
 
     - name: Restore dependency cache