diff --git a/action.yml b/action.yml
index 89b02a8..3cb5b70 100644
--- a/action.yml
+++ b/action.yml
@@ -15,7 +15,7 @@ inputs:
   BEFORE:
     description: "The SHA of the last pushed commit (automatically set)"
     required: true
-    default: "${{ github.event.before }}"     
+    default: "${{ github.event.before || github.base_ref }}"
   COMMITS:
     description: "An array of commit objects describing the pushed commits"
     required: true