diff --git a/src/pretix/base/shredder.py b/src/pretix/base/shredder.py
index 27597122ba..e373b1e7d8 100644
--- a/src/pretix/base/shredder.py
+++ b/src/pretix/base/shredder.py
@@ -383,9 +383,10 @@ class QuestionAnswerShredder(BaseDataShredder):
             d = le.parsed_data
             if 'data' in d:
                 for i, row in enumerate(d['data']):
-                    for f in row:
-                        if f not in ('attendee_name', 'attendee_email'):
-                            d['data'][i][f] = '█'
+                    if isinstance(d['data'], dict):
+                        for f in row:
+                            if f not in ('attendee_name', 'attendee_email'):
+                                d['data'][i][f] = '█'
                 le.data = json.dumps(d)
                 le.shredded = True
                 le.save(update_fields=['data', 'shredded'])