diff --git a/tests/domain/epc/test_main_fuel_overlay.py b/tests/domain/epc/test_main_fuel_overlay.py
index f3cf0007..3f6bfdeb 100644
--- a/tests/domain/epc/test_main_fuel_overlay.py
+++ b/tests/domain/epc/test_main_fuel_overlay.py
@@ -40,3 +40,13 @@ def test_fuels_decode_to_their_modern_not_community_codes(
     assert simulation is not None
     assert simulation.heating is not None
     assert simulation.heating.main_fuel_type == code
+
+
+def test_community_mains_gas_is_a_distinct_fuel_code() -> None:
+    # Act
+    simulation = fuel_overlay_for("mains gas (community)", 0)
+
+    # Assert — community mains gas is code 20, distinct from 26 (not community).
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.main_fuel_type == 20