diff --git a/app/models/user_session.rb b/app/models/user_session.rb
index e7556cb..ec55ada 100644
--- a/app/models/user_session.rb
+++ b/app/models/user_session.rb
@@ -1,3 +1,6 @@
 class UserSession < Authlogic::Session::Base
   # configuration here, see documentation for sub modules of Authlogic::Session
-end
\ No newline at end of file
+  def to_key
+    new_record? ? nil : [ self.send(self.class.primary_key) ]
+  end
+end