diff --git a/src/void_map.h b/src/void_map.h
--- a/src/void_map.h
+++ b/src/void_map.h
@@ -12,7 +12,7 @@ static inline void MakeVoid(TileIndex t)
 	_m[t].m3 = 0;
 	_m[t].m4 = 0;
 	_m[t].m5 = 0;
-	_m[t].extra = 0;
+	_m[t].m6 = 0;
 }
 
 #endif /* VOID_MAP_H */