diff --git a/changelog_entry.yaml b/changelog_entry.yaml
index e69de29bb..53011553f 100644
--- a/changelog_entry.yaml
+++ b/changelog_entry.yaml
@@ -0,0 +1,6 @@
+- bump: patch
+  changes:
+    fixed:
+    - Projector.transform now raises NotImplementedError
+    added:
+    - regression test ensuring base Projector.transform raises
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()
diff --git a/tests/core/test_projectors.py b/tests/core/test_projectors.py
index a2e3444af..9b9c8adb5 100644
--- a/tests/core/test_projectors.py
+++ b/tests/core/test_projectors.py
@@ -1,11 +1,21 @@
 import numpy as np
+import pytest
 
 from policyengine_core.entities import build_entity
 from policyengine_core.model_api import ETERNITY, Enum, Variable
 from policyengine_core.simulations.simulation_builder import SimulationBuilder
+
 from policyengine_core.taxbenefitsystems import TaxBenefitSystem
 
 
+def test_base_projector_transform_raises():
+    from policyengine_core.projectors.projector import Projector
+
+    projector = Projector()
+    with pytest.raises(NotImplementedError):
+        projector.transform([])
+
+
 def test_shortcut_to_containing_entity_provided():
     """
     Tests that, when an entity provides a containing entity,