diff --git a/datatypes/magicplan/domain/tests/test_mapper.py b/datatypes/magicplan/domain/tests/test_mapper.py
index 7632e7ef..053c3d7f 100644
--- a/datatypes/magicplan/domain/tests/test_mapper.py
+++ b/datatypes/magicplan/domain/tests/test_mapper.py
@@ -4,8 +4,8 @@ from typing import Any
 
 import pytest
 
-from datatypes.magicplan.api.response import MagicPlanPlan
-from datatypes.magicplan.domain.mapper import map_plan
+from datatypes.magicplan.api.response import MagicPlanPlan, Symbol, Vec3, WallItem
+from datatypes.magicplan.domain.mapper import _map_window, map_plan
 from datatypes.magicplan.domain.models import Plan
 
 FIXTURE_DIR = Path(__file__).parents[4] / "backend" / "magic_plan"
@@ -240,6 +240,20 @@ def plan_new() -> Plan:
     return map_plan(MagicPlanPlan.model_validate(payload["data"]))
 
 
+def test_window_with_no_custom_fields_has_no_ventilation() -> None:
+    wi = WallItem(
+        uid="test",
+        symbol=Symbol(id="windowcasement", name="Casement Window", valid=True),
+        size=Vec3(x=1.0, y=0.0, z=1.2),
+        position=Vec3(x=0.0, y=0.0, z=0.0),
+        rotation=Vec3(x=0.0, y=0.0, z=0.0),
+    )
+
+    window = _map_window(wi)
+
+    assert window.ventilation is None
+
+
 def test_kitchen_window_has_ventilation(plan_new: Plan) -> None:
     # Arrange — Kitchen is floor 0 room 0; its only window is a windowcasement
     # with custom_displayable_fields populated in the new fixture.