diff --git a/action.yml b/action.yml
index f99fa23..e3f92b0 100644
--- a/action.yml
+++ b/action.yml
@@ -7,7 +7,7 @@ inputs:
   base-ref:
     description: 'Base reference for API compatibility comparison (default: base branch)'
     required: false
-    default: "origin/${GITHUB_BASE_REF}"
+    default: "${{ github.event.pull_request.base.sha || github.event.merge_group.base_sha }}"
   version:
     description: 'Version of go-apidiff to use'
     required: false