diff --git a/app/models/dunlop/source_file_model.rb b/app/models/dunlop/source_file_model.rb
index b9095ef..2852b17 100644
--- a/app/models/dunlop/source_file_model.rb
+++ b/app/models/dunlop/source_file_model.rb
@@ -179,8 +179,8 @@ module Dunlop::SourceFileModel
 
     # braindump towards state => processed support for source-files
     def latest_processed
-      if base_class == self
-        join_select = processed.select('MAX(id) AS max_id').group(:sti_type)
+      if base_class == self # return a scope having only the latest processed source-files
+        join_select = processed.select('MAX(id) AS max_id').group(inheritance_column)
         #join_select = processed.selecting{ id.maximum.as('max_id')}.group(:sti_type)
         joins("INNER JOIN (#{join_select.to_sql}) tmp ON id = tmp.max_id")
       else # return the latest process of the specific source-file class