diff --git a/c3l_membership/views.py b/c3l_membership/views.py
--- a/c3l_membership/views.py
+++ b/c3l_membership/views.py
@@ -1,9 +1,10 @@
 import re
 import subprocess
 from datetime import date
+from typing import Any, Dict, Optional, cast
 
 import requests
-from flask import Blueprint, current_app, g, render_template, request
+from flask import Blueprint, Response, current_app, g, render_template, request
 from flask_babel import gettext
 from flask_weasyprint import HTML, render_pdf
 
@@ -16,19 +17,19 @@ xml_template = "<member><numm>{name}</nu
 
 
 @root_page.url_defaults
-def add_lang_code(endpoint, values):
+def add_lang_code(endpoint: Any, values: Dict[str, Any]) -> None:
     values.setdefault("lang_code", g.lang_code)
 
 
 @root_page.url_value_preprocessor
-def pull_lang_code(endpoint, values):
+def pull_lang_code(endpoint: Optional[str], values: Optional[Dict[Any, Any]]) -> None:
     lang_code = values.pop("lang_code")
     if lang_code != "favicon.ico":
         g.lang_code = lang_code
 
 
 @root_page.route("/", methods=("GET", "POST"))
-def index():
+def index() -> Response:
     form = MembershipForm()
 
     choices = [
@@ -139,5 +140,4 @@ def index():
                 HTML(string=html),
                 download_filename=f"C3L_Membership_{form.username.data}.pdf",
             )
-
     return render_template("index.html", form=form, crypto_error=False)