diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 3d7c9901a8e..07369ecad27 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -28,7 +28,7 @@ jobs:
       - name: Check for source changes
         id: check
         run: |
-          if [ -z "GITHUB_BASE_REF" ]; then
+          if [ -z "$GITHUB_BASE_REF" ]; then
             echo '::set-output name=run_tests::true'
           else
             git fetch origin $GITHUB_BASE_REF --depth=1