diff --git a/lib/action_dispatch/session/active_record_store.rb b/lib/action_dispatch/session/active_record_store.rb
index 99bd8e2..67c0573 100644
--- a/lib/action_dispatch/session/active_record_store.rb
+++ b/lib/action_dispatch/session/active_record_store.rb
@@ -78,7 +78,7 @@ def write_session(request, sid, session_data, options)
         logger.silence do
           record, sid = get_session_model(request, sid)
           record.data = session_data
-          return false unless record.save
+          return sid if record.changed? and not record.save
 
           session_data = record.data
           if session_data && session_data.respond_to?(:each_value)