diff --git a/src/viewport_func.h b/src/viewport_func.h
--- a/src/viewport_func.h
+++ b/src/viewport_func.h
@@ -74,4 +74,6 @@ void UpdateAllVirtCoords();
 
 extern Point _tile_fract_coords;
 
+void MarkTileDirtyByTile(TileIndex tile);
+
 #endif /* VIEWPORT_FUNC_H */