diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 666267c9c0..67a01209d7 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -25,7 +25,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           # sometimes checkout action doesn't result in clean directory?
-          ref: ${{ github.event.pull_request.head.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.ref }}
           submodules: 'recursive'
       - run: git status --ignored
       - run: brew install coreutils findutils gnu-sed gawk grep rename sphinx-doc