diff --git a/python/taichi/lang/mesh.py b/python/taichi/lang/mesh.py
index 9ed333293be35..6b9e474b1ae75 100644
--- a/python/taichi/lang/mesh.py
+++ b/python/taichi/lang/mesh.py
@@ -606,7 +606,8 @@ def update_relation(tree, ctx):
         name_to_order = {"verts": 0, "edges": 1, "faces": 2, "cells": 3}
         for visit in x.visits:
             if visit[1] in name_to_order and visit[2] in name_to_order:
-                visit[0].update_relation(name_to_order[visit[1]], name_to_order[visit[2]])
+                visit[0].update_relation(name_to_order[visit[1]],
+                                         name_to_order[visit[2]])
 
 
 def TriMesh():