diff --git a/action.yml b/action.yml
index 2626a9bf..94488f23 100644
--- a/action.yml
+++ b/action.yml
@@ -18,7 +18,7 @@ inputs:
       When 'true', existing entries will be read from the cache but no entries will be written.
       By default this value is 'false' for workflows on the GitHub default branch and 'true' for workflows on other branches.
     required: false
-    default: ${{ github.ref_name != github.event.repository.default_branch }}
+    default: ${{ github.event.repository && github.ref_name != github.event.repository.default_branch }}
 
   cache-write-only:
     description: |