diff --git a/src/pretix/control/views/orders.py b/src/pretix/control/views/orders.py
index 5919d9d7e..356c4fb3e 100644
--- a/src/pretix/control/views/orders.py
+++ b/src/pretix/control/views/orders.py
@@ -140,8 +140,8 @@ class OrderDetail(OrderView):
         def keyfunc(pos):
             if (pos.item.admission and self.request.event.settings.attendee_names_asked) \
                     or pos.item.questions.all():
-                return pos.id, 0, 0, 0, 0, None
-            return 0, pos.item_id, pos.variation_id, pos.price, pos.tax_rate, pos.voucher
+                return pos.id, 0, 0, 0, 0, 0
+            return 0, pos.item_id, pos.variation_id, pos.price, pos.tax_rate, (pos.voucher_id or 0)
 
         positions = []
         for k, g in groupby(sorted(list(cartpos), key=keyfunc), key=keyfunc):
diff --git a/src/pretix/presale/views/__init__.py b/src/pretix/presale/views/__init__.py
index 8ad0dc397..73a9af3e0 100644
--- a/src/pretix/presale/views/__init__.py
+++ b/src/pretix/presale/views/__init__.py
@@ -48,8 +48,8 @@ class CartMixin:
         def keyfunc(pos):
             if answers and ((pos.item.admission and self.request.event.settings.attendee_names_asked)
                             or pos.item.questions.all()):
-                return pos.id, 0, 0, 0, None
-            return 0, pos.item_id, pos.variation_id, pos.price, pos.voucher
+                return pos.id, 0, 0, 0, 0
+            return 0, pos.item_id, pos.variation_id, pos.price, (pos.voucher_id or 0)
 
         positions = []
         for k, g in groupby(sorted(list(cartpos), key=keyfunc), key=keyfunc):