diff --git a/.github/workflows/staging-promotion-metadata.yml b/.github/workflows/staging-promotion-metadata.yml
index 63591d83..76b8326b 100644
--- a/.github/workflows/staging-promotion-metadata.yml
+++ b/.github/workflows/staging-promotion-metadata.yml
@@ -31,10 +31,12 @@ jobs:
       github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout base branch
+      - name: Checkout workflow source
         uses: actions/checkout@v6
         with:
-          ref: ${{ github.event_name == 'workflow_dispatch' && 'main' || github.event.pull_request.base.ref }}
+          # For chained promotion PRs, the script lives on the trusted PR head,
+          # not necessarily on the older promotion branch used as the PR base.
+          ref: ${{ github.event_name == 'workflow_dispatch' && 'main' || github.event.pull_request.head.sha }}
           fetch-depth: 0
           fetch-tags: true