diff --git a/.github/workflows/clean-up-closed-prs.yml b/.github/workflows/clean-up-closed-prs.yml
index 7b15edb18300..03365829eafd 100644
--- a/.github/workflows/clean-up-closed-prs.yml
+++ b/.github/workflows/clean-up-closed-prs.yml
@@ -57,6 +57,7 @@ jobs:
   delete-branch:
     if: >
       github.repository_owner == 'Homebrew' &&
+      github.event.pull_request.head.repo.full_name == github.repository &&
       !github.event.pull_request.merged
     runs-on: ubuntu-latest
     # Ignore errors as branch may already be deleted