diff --git a/src/pretix/base/models/items.py b/src/pretix/base/models/items.py
index 22d584c5e6..618ea3a9ac 100644
--- a/src/pretix/base/models/items.py
+++ b/src/pretix/base/models/items.py
@@ -1391,7 +1391,7 @@ class Quota(LoggedModel):
 
     @staticmethod
     def clean_variations(items, variations):
-        for variation in variations:
+        for variation in (variations or []):
             if variation.item not in items:
                 raise ValidationError(_('All variations must belong to an item contained in the items list.'))
                 break