diff --git a/tests/repositories/property/test_landlord_override_overlays.py b/tests/repositories/property/test_landlord_override_overlays.py
index b2b49d55..1f790aa8 100644
--- a/tests/repositories/property/test_landlord_override_overlays.py
+++ b/tests/repositories/property/test_landlord_override_overlays.py
@@ -112,6 +112,23 @@ def test_water_heating_row_produces_a_heating_overlay() -> None:
     assert overlays[0].heating.water_heating_fuel == 26
 
 
+def test_main_heating_system_row_produces_a_heating_overlay() -> None:
+    # Arrange
+    overrides = ResolvedPropertyOverrides(
+        rows=(
+            ResolvedPropertyOverride("main_heating_system", 0, "Gas boiler, combi"),
+        )
+    )
+
+    # Act
+    overlays = overlays_from(overrides)
+
+    # Assert
+    assert len(overlays) == 1
+    assert overlays[0].heating is not None
+    assert overlays[0].heating.sap_main_heating_code == 104
+
+
 def test_unresolvable_rows_are_skipped() -> None:
     # Arrange — an "Unknown" property type and an unmapped wall material.
     overrides = ResolvedPropertyOverrides(