diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d5fae44..7c7e2d9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -46,7 +46,7 @@ jobs:
     - name: Run PHPCS on all Core files
       run: |
         touch $GITHUB_WORKSPACE/tmp.php
-        export CHANGED_FILES=$(git diff --name-only --diff-filter=AM ${{ github.base_ref }} | tr '\n' ' ')
+        export CHANGED_FILES=$(git diff --name-only --diff-filter=AM remotes/origin/${{ github.base_ref }} | tr '\n' ' ')
         composer run-script phpcs $GITHUB_WORKSPACE/tmp.php $(echo $CHANGED_FILES) -- -n | cs2pr
 
   phpunit: