diff --git a/lib/submitters.rb b/lib/submitters.rb
index 171a2439..bfd168ad 100644
--- a/lib/submitters.rb
+++ b/lib/submitters.rb
@@ -118,7 +118,7 @@ module Submitters
   end
 
   def build_document_filename(submitter, blob, filename_format)
-    return blob.filename if filename_format.blank?
+    return blob.filename.to_s if filename_format.blank?
 
     filename = ReplaceEmailVariables.call(filename_format, submitter:)