diff --git a/app/account_service.py b/app/account_service.py
index a7ed0c4..fd5f7f6 100644
--- a/app/account_service.py
+++ b/app/account_service.py
@@ -1,4 +1,5 @@
 from flask import *
+from markupsafe import escape
 from Login import check_username_availability, verify_user, add_user, get_expiry_date, change_password, WarningMessage
 
 
diff --git a/app/admin_service.py b/app/admin_service.py
index 7f41dd5..c461af9 100644
--- a/app/admin_service.py
+++ b/app/admin_service.py
@@ -1,5 +1,6 @@
 # System Library
 from flask import *
+from markupsafe import escape
 
 # Personal library
 from Yaml import yml
diff --git a/app/main.py b/app/main.py
index 5d5f7cc..f43b36b 100644
--- a/app/main.py
+++ b/app/main.py
@@ -5,7 +5,8 @@
 # Copyright 2019 (C) Hui Lan <hui.lan@cantab.net>
 # Written permission must be obtained from the author for commercial uses.
 ###########################################################################
-from flask import escape, abort
+from flask import abort
+from markupsafe import escape
 from Login import *
 from Article import *
 import Yaml
diff --git a/requirements.txt b/requirements.txt
index 338b71c..8018227 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-Flask==1.1.2
+Flask==2.3.2
 selenium==3.141.0
 PyYAML~=6.0
 pony==0.7.16