diff --git a/datatypes/magicplan/domain/tests/test_mapper.py b/datatypes/magicplan/domain/tests/test_mapper.py
index 053c3d7f..09e8aa28 100644
--- a/datatypes/magicplan/domain/tests/test_mapper.py
+++ b/datatypes/magicplan/domain/tests/test_mapper.py
@@ -254,6 +254,15 @@ def test_window_with_no_custom_fields_has_no_ventilation() -> None:
     assert window.ventilation is None
 
 
+def test_toilet_door_has_ventilation_undercut(plan_new: Plan) -> None:
+    # Toilet is floor 0 room 2; its doorhinged has Door Undercut (mm) = 70
+    toilet_doors = plan_new.floors[0].rooms[2].doors
+    hinged = next(d for d in toilet_doors if d.ventilation is not None)
+
+    assert hinged.ventilation is not None
+    assert hinged.ventilation.undercut_mm == 70.0
+
+
 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.