diff --git a/datatypes/magicplan/domain/tests/test_mapper.py b/datatypes/magicplan/domain/tests/test_mapper.py
index 85467267..1d2b68b4 100644
--- a/datatypes/magicplan/domain/tests/test_mapper.py
+++ b/datatypes/magicplan/domain/tests/test_mapper.py
@@ -254,6 +254,16 @@ def test_window_with_no_custom_fields_has_no_ventilation() -> None:
     assert window.ventilation is None
 
 
+def test_glass_door_ventilation_opening_type(plan_new: Plan) -> None:
+    # The doorglass in Living/Dining Room carries Opening Type = "External.Door"
+    # in its custom_displayable_fields.
+    room = plan_new.floors[0].rooms[1]
+    glass = next(w for w in room.windows if w.opening_type == "doorglass")
+
+    assert glass.ventilation is not None
+    assert glass.ventilation.opening_type == "External.Door"
+
+
 def test_doorglass_is_classified_as_window(plan_new: Plan) -> None:
     # Living/Dining Room (floor 0, room 1) has one doorglass wall item.
     # It must appear in room.windows, not room.doors.