diff --git a/tests/backend/app/modelling/test_property_filters.py b/tests/backend/app/modelling/test_property_filters.py
index 0ee70154e..223696dd5 100644
--- a/tests/backend/app/modelling/test_property_filters.py
+++ b/tests/backend/app/modelling/test_property_filters.py
@@ -240,6 +240,24 @@ def test_property_without_epc_falls_back_to_the_legacy_column(
     assert [p.property_id for p in resolved] == [legacy]
 
 
+def test_unknown_is_a_selectable_property_type_bucket(db_engine: Engine) -> None:
+    # arrange — one property resolvable at no level, one resolvable
+    with Session(db_engine) as session:
+        unknowable = _seed_property(session, portfolio_id=814)
+        typed = _seed_property(session, portfolio_id=814)
+        _seed_epc(session, property_id=typed, property_type="House")
+
+        # act
+        resolved = resolve_filtered_property_ids(
+            session,
+            portfolio_id=814,
+            filters=PropertyGroupFilters(property_types=["Unknown"]),
+        )
+
+    # assert
+    assert [p.property_id for p in resolved] == [unknowable]
+
+
 def test_postcode_filter_matches_exactly(db_engine: Engine) -> None:
     # arrange
     with Session(db_engine) as session: