diff --git a/src/newgrf_airporttiles.h b/src/newgrf_airporttiles.h
--- a/src/newgrf_airporttiles.h
+++ b/src/newgrf_airporttiles.h
@@ -24,7 +24,7 @@ struct AirportTileScopeResolver : public
 	byte airport_id;     ///< Type of airport for which the callback is run.
 	TileIndex tile;      ///< Tile for the callback, only valid for airporttile callbacks.
 
-	AirportTileScopeResolver(ResolverObject *ro, const AirportTileSpec *ats, TileIndex tile, Station *st);
+	AirportTileScopeResolver(ResolverObject &ro, const AirportTileSpec *ats, TileIndex tile, Station *st);
 
 	/* virtual */ uint32 GetRandomBits() const;
 	/* virtual */ uint32 GetVariable(byte variable, uint32 parameter, bool *available) const;