diff --git a/docs/src/ci.md b/docs/src/ci.md
index fcb9366b8b..97ea4ad8d2 100644
--- a/docs/src/ci.md
+++ b/docs/src/ci.md
@@ -433,6 +433,8 @@ jobs:
     steps:
     - uses: actions/checkout@v4
       with:
+        # Force a non-shallow checkout, so that we can reference $GITHUB_BASE_REF.
+        # See https://github.com/actions/checkout for more details.
         fetch-depth: 0
     - uses: actions/setup-node@v4
       with: