diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0f03c1e8d005b5fc1e09acb1ae22cba62bf93300..2b87ac37aa1cb54f4a56c8c3b91a3ffd4f55f15f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -139,7 +139,7 @@ If you want to use information within the `file_id` to name outputs in your `scr
       file_prefix = file_id.values()[0]
     break
     default:
-      file_id
+      file_prefix = file_id
     break
   }
 ```