diff --git a/src/newgrf_house.h b/src/newgrf_house.h
--- a/src/newgrf_house.h
+++ b/src/newgrf_house.h
@@ -44,7 +44,7 @@ void DrawNewHouseTile(TileInfo *ti, Hous
 void AnimateNewHouseTile(TileIndex tile);
 void ChangeHouseAnimationFrame(const struct GRFFile *file, TileIndex tile, uint16 callback_result);
 
-uint16 GetHouseCallback(CallbackID callback, uint32 param1, uint32 param2, HouseID house_id, Town *town, TileIndex tile, bool not_yet_constructed = false, uint8 initial_random_bits = 0);
+uint16 GetHouseCallback(CallbackID callback, uint32 param1, uint32 param2, HouseID house_id, const Town *town, TileIndex tile, bool not_yet_constructed = false, uint8 initial_random_bits = 0);
 
 bool CanDeleteHouse(TileIndex tile);