diff --git a/.github/workflows/build_size_report.yml b/.github/workflows/build_size_report.yml
index 7dc22bfd8..55f7f09ca 100644
--- a/.github/workflows/build_size_report.yml
+++ b/.github/workflows/build_size_report.yml
@@ -9,6 +9,8 @@ jobs:
     timeout-minutes: 30
     steps:
       - uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
       - uses: preactjs/compressed-size-action@v2
         with:
           strip-hash: "\\b\\w{8}\\."