diff --git a/src/pretix/api/serializers/event.py b/src/pretix/api/serializers/event.py
index 786f3ffc9..fd8e07511 100644
--- a/src/pretix/api/serializers/event.py
+++ b/src/pretix/api/serializers/event.py
@@ -580,6 +580,7 @@ class EventSettingsSerializer(SettingsSerializer):
         'locale',
         'region',
         'last_order_modification_date',
+        'allow_modifications_after_checkin',
         'show_quota_left',
         'waiting_list_enabled',
         'waiting_list_hours',
diff --git a/src/pretix/base/models/orders.py b/src/pretix/base/models/orders.py
index 1cfd22765..7af9b5d1b 100644
--- a/src/pretix/base/models/orders.py
+++ b/src/pretix/base/models/orders.py
@@ -666,6 +666,8 @@ class Order(LockModel, LoggedModel):
         related to the order. This checks order status and modification deadlines. It also
         returns ``False`` if there are no questions that can be answered.
         """
+        from .checkin import Checkin
+
         if self.status not in (Order.STATUS_PENDING, Order.STATUS_PAID, Order.STATUS_EXPIRED):
             return False
 
@@ -681,10 +683,21 @@ class Order(LockModel, LoggedModel):
 
         if modify_deadline is not None and now() > modify_deadline:
             return False
+
+        positions = list(
+            self.positions.all().annotate(
+                has_checkin=Exists(Checkin.objects.filter(position_id=OuterRef('pk')))
+            ).select_related('item').prefetch_related('item__questions')
+        )
+        if not self.event.settings.allow_modifications_after_checkin:
+            for cp in positions:
+                if cp.has_checkin:
+                    return False
+
         if self.event.settings.get('invoice_address_asked', as_type=bool):
             return True
         ask_names = self.event.settings.get('attendee_names_asked', as_type=bool)
-        for cp in self.positions.all().prefetch_related('item__questions'):
+        for cp in positions:
             if (cp.item.admission and ask_names) or cp.item.questions.all():
                 return True
 
diff --git a/src/pretix/base/settings.py b/src/pretix/base/settings.py
index 525b424ac..78cb8e5f6 100644
--- a/src/pretix/base/settings.py
+++ b/src/pretix/base/settings.py
@@ -1082,6 +1082,15 @@ DEFAULTS = {
             help_text=_('If your event series has more than 50 dates in the future, only the month or week calendar can be used.')
         ),
     },
+    'allow_modifications_after_checkin': {
+        'default': 'False',
+        'type': bool,
+        'form_class': forms.BooleanField,
+        'serializer_class': serializers.BooleanField,
+        'form_kwargs': dict(
+            label=_("Allow customers to modify their information after they checked in."),
+        )
+    },
     'last_order_modification_date': {
         'default': None,
         'type': RelativeDateWrapper,
diff --git a/src/pretix/control/forms/event.py b/src/pretix/control/forms/event.py
index 64e9b209c..44f294afa 100644
--- a/src/pretix/control/forms/event.py
+++ b/src/pretix/control/forms/event.py
@@ -457,6 +457,7 @@ class EventSettingsForm(SettingsForm):
         'banner_text_bottom',
         'order_email_asked_twice',
         'last_order_modification_date',
+        'allow_modifications_after_checkin',
         'checkout_show_copy_answers_button',
         'primary_color',
         'theme_color_success',
diff --git a/src/pretix/control/templates/pretixcontrol/event/settings.html b/src/pretix/control/templates/pretixcontrol/event/settings.html
index 535b06588..e5bba833d 100644
--- a/src/pretix/control/templates/pretixcontrol/event/settings.html
+++ b/src/pretix/control/templates/pretixcontrol/event/settings.html
@@ -243,6 +243,7 @@
                 {% bootstrap_field form.presale_end layout="control" %}
                 {% bootstrap_field sform.show_items_outside_presale_period layout="control" %}
                 {% bootstrap_field sform.last_order_modification_date layout="control" %}
+                {% bootstrap_field sform.allow_modifications_after_checkin layout="control" %}
             </fieldset>
             <fieldset>
                 <legend>{% trans "Display" %}</legend>