diff --git a/lib/abf_worker/base_observer.rb b/lib/abf_worker/base_observer.rb
index 2e2b68d2f..79af23b49 100644
--- a/lib/abf_worker/base_observer.rb
+++ b/lib/abf_worker/base_observer.rb
@@ -34,7 +34,7 @@ module AbfWorker
     end
 
     def sort_results_and_save(results, item = subject)
-      item.results = results.sort_by{ |r| [r['timestamp'], r['file_name']] }
+      item.results = results.sort_by{ |r| [r['timestamp'].to_s, r['file_name'].to_s] }
       item.save(validate: false)
     end