diff --git a/c3l_membership/views.py b/c3l_membership/views.py
--- a/c3l_membership/views.py
+++ b/c3l_membership/views.py
@@ -73,7 +73,9 @@ def index():
             xml_data["status"] = "Regular"
 
         xml_data["name"] = form.fullname.data
-        xml_data["birthday"] = form.birthday.data
+        xml_data["birthday"] = (
+            form.birthday.data if form.birthday.data is not None else date(9999, 12, 12)
+        )
         xml_data["username"] = form.username.data
         xml_data["email"] = form.email.data
         xml_data["address"] = " ".join(