diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 239e49a..683f70a 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -12,7 +12,7 @@ jobs:
   test-cpp:
     runs-on: ubuntu-latest
     env:
-      COMMIT_SHA: ${{ github.event.pull_request.head.sha || GITHUB_SHA }}
+      COMMIT_SHA: ${{ github.event.pull_request.head.sha }} || $GITHUB_SHA
     steps:
       - name: test on remote server
         uses: appleboy/ssh-action@master