diff --git a/policyengine_core/projectors/projector.py b/policyengine_core/projectors/projector.py
index 7ac30bb6b..b92da7cc1 100644
--- a/policyengine_core/projectors/projector.py
+++ b/policyengine_core/projectors/projector.py
@@ -41,4 +41,4 @@ def transform_and_bubble_up(self, result):
             return self.parent.transform_and_bubble_up(transformed_result)
 
     def transform(self, result: ArrayLike):
-        return NotImplementedError()
+        raise NotImplementedError()