diff --git a/ir.py b/ir.py
index d3ec250..018dd8e 100644
--- a/ir.py
+++ b/ir.py
@@ -14,9 +14,9 @@ class Rule(metaclass=PoolMeta):
         """ list of models to add 'user_id' to context
         """
         result = super(Rule, cls)._context_modelnames()
-        result.extend([
+        return result | {
             'cashbook.planner',
-            'cashbook.planner.nextrun'])
-        return result
+            'cashbook.planner.nextrun',
+        }
 
 # end Rule