diff --git a/ihatemoney/api/common.py b/ihatemoney/api/common.py
index 44727f5a..caf8148b 100644
--- a/ihatemoney/api/common.py
+++ b/ihatemoney/api/common.py
@@ -3,7 +3,7 @@ from functools import wraps
 from flask import current_app, request
 from flask_restful import Resource, abort
 from werkzeug.security import check_password_hash
-from wtforms.fields.core import BooleanField
+from wtforms.fields import BooleanField
 
 from ihatemoney.currency_convertor import CurrencyConverter
 from ihatemoney.emails import send_creation_email
diff --git a/ihatemoney/forms.py b/ihatemoney/forms.py
index fe966778..0e99f534 100644
--- a/ihatemoney/forms.py
+++ b/ihatemoney/forms.py
@@ -9,9 +9,23 @@ from flask_wtf.file import FileAllowed, FileField, FileRequired
 from flask_wtf.form import FlaskForm
 from markupsafe import Markup
 from werkzeug.security import check_password_hash, generate_password_hash
-from wtforms.fields.core import Label, SelectField, SelectMultipleField
-from wtforms.fields.html5 import DateField, DecimalField, URLField
-from wtforms.fields.simple import BooleanField, PasswordField, StringField, SubmitField
+from wtforms.fields import (
+    BooleanField,
+    DateField,
+    DecimalField,
+    Label,
+    PasswordField,
+    SelectField,
+    SelectMultipleField,
+    StringField,
+    SubmitField,
+)
+
+try:
+    # Compat for WTForms <= 2.3.3
+    from wtforms.fields.html5 import URLField
+except ModuleNotFoundError:
+    from wtforms.fields import URLField
 from wtforms.validators import (
     URL,
     DataRequired,
@@ -312,6 +326,7 @@ class BillForm(FlaskForm):
     original_currency = SelectField(_("Currency"), validators=[DataRequired()])
     external_link = URLField(
         _("External link"),
+        default="",
         validators=[Optional(), URL()],
         description=_("A link to an external document, related to this bill"),
     )
diff --git a/setup.cfg b/setup.cfg
index 5cedf791..ded7642a 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -35,7 +35,7 @@ install_requires =
     Flask-SQLAlchemy>=2.4,<3
     Flask-Talisman>=0.8,<1
     Flask-WTF>=0.14.3,<2
-    WTForms>=2.3.1,<2.4
+    WTForms>=2.3.1,<3.1
     Flask>=2,<3
     itsdangerous>=2,<3
     Jinja2>=3,<4