diff --git a/.github/workflows/preview_cleanup.yml b/.github/workflows/preview_cleanup.yml
index 93c4e1aa..8e38f289 100644
--- a/.github/workflows/preview_cleanup.yml
+++ b/.github/workflows/preview_cleanup.yml
@@ -12,7 +12,7 @@ jobs:
         runs-on: ubuntu-latest
         if: github.event.label.name == 'use-preview'
         env:
-            BASE: refs/pull/${{ github.event.pull_request.number }}
+            BASE: ./refs/pull/${{ github.event.pull_request.number }}
 
         steps:
             - uses: actions/checkout@v2