diff --git a/src/pretix/api/views/checkin.py b/src/pretix/api/views/checkin.py
index 325f5017f..afd9ce9ba 100644
--- a/src/pretix/api/views/checkin.py
+++ b/src/pretix/api/views/checkin.py
@@ -152,6 +152,11 @@ class CheckinListViewSet(viewsets.ModelViewSet):
     @action(detail=True, methods=['POST'], url_name='failed_checkins')
     @transaction.atomic()
     def failed_checkins(self, *args, **kwargs):
+        additional_log_data = {}
+        if 'debug_data' in self.request.data:
+            # Intentionally undocumented, might be removed again
+            additional_log_data['debug_data'] = self.request.data.pop('debug_data')
+
         serializer = FailedCheckinSerializer(
             data=self.request.data,
             context={'event': self.request.event}
@@ -194,14 +199,16 @@ class CheckinListViewSet(viewsets.ModelViewSet):
                 'reason_explanation': c.error_explanation,
                 'datetime': c.datetime,
                 'type': c.type,
-                'list': c.list.pk
+                'list': c.list.pk,
+                **additional_log_data,
             }, user=self.request.user, auth=self.request.auth)
         else:
             self.request.event.log_action('pretix.event.checkin.unknown', data={
                 'datetime': c.datetime,
                 'type': c.type,
                 'list': c.list.pk,
-                'barcode': c.raw_barcode
+                'barcode': c.raw_barcode,
+                **additional_log_data,
             }, user=self.request.user, auth=self.request.auth)
 
         return Response(serializer.data, status=201)
diff --git a/src/tests/api/test_checkin.py b/src/tests/api/test_checkin.py
index 1a4bbff59..ef79d2196 100644
--- a/src/tests/api/test_checkin.py
+++ b/src/tests/api/test_checkin.py
@@ -35,7 +35,7 @@ from tests.const import SAMPLE_PNG
 
 from pretix.api.serializers.item import QuestionSerializer
 from pretix.base.models import (
-    Checkin, CheckinList, InvoiceAddress, Order, OrderPosition,
+    Checkin, CheckinList, InvoiceAddress, Order, OrderPosition, LogEntry,
 )
 
 
@@ -1128,11 +1128,17 @@ def test_store_failed(token_client, organizer, clist, event, order):
     ), {
         'raw_barcode': '123456',
         'nonce': '4321',
-        'error_reason': 'invalid'
+        'error_reason': 'invalid',
+        'debug_data': {'foo': 'bar'},
     }, format='json')
     assert resp.status_code == 201
     with scopes_disabled():
         assert Checkin.all.filter(successful=False).exists()
+        for le in LogEntry.objects.filter():
+            print(le.parsed_data)
+        assert LogEntry.objects.filter(action_type='pretix.event.checkin.unknown').first().parsed_data['debug_data'] == {
+            'foo': 'bar'
+        }
 
     resp = token_client.post('/api/v1/organizers/{}/events/{}/checkinlists/{}/failed_checkins/'.format(
         organizer.slug, event.slug, clist.pk,
@@ -1162,7 +1168,7 @@ def test_store_failed(token_client, organizer, clist, event, order):
         'raw_barcode': '123456',
         'nonce': '1234',
         'position': p.pk,
-        'error_reason': 'unpaid'
+        'error_reason': 'unpaid',
     }, format='json')
     assert resp.status_code == 201
     with scopes_disabled():