diff --git a/c3l_membership/forms.py b/c3l_membership/forms.py
--- a/c3l_membership/forms.py
+++ b/c3l_membership/forms.py
@@ -63,30 +63,30 @@ class MembershipForm(FlaskForm):
         validators=[InputRequired(lazy_gettext("Please select one of the options!"))],
     )
 
-    birthday = DateField(lazy_gettext("Birthday"))
+    birthday = DateField(lazy_gettext("Birthday"), validators=[Optional()])
 
     street = StringField(
         lazy_gettext("Nr., Street"),
-        validators=[Length(max=4000)],
+        validators=[Optional(), Length(max=4000)],
     )
     zip = StringField(
         lazy_gettext("Postal Code"),
-        validators=[Length(max=30)],
+        validators=[Optional(), Length(max=30)],
     )
 
     city = StringField(
         lazy_gettext("City/Town"),
-        validators=[Length(max=500)],
+        validators=[Optional(), Length(max=500)],
     )
 
     state = StringField(
         lazy_gettext("State/County/Province"),
-        validators=[Length(max=500)],
+        validators=[Optional(), Length(max=500)],
     )
 
     country = StringField(
         lazy_gettext("Country"),
-        validators=[Length(max=500)],
+        validators=[Optional(), Length(max=500)],
     )
 
     terms = BooleanField(