diff --git a/src/pretix/base/payment.py b/src/pretix/base/payment.py
index 67e54a824..ab1fa0f9f 100644
--- a/src/pretix/base/payment.py
+++ b/src/pretix/base/payment.py
@@ -1231,8 +1231,8 @@ class ManualPayment(BasePaymentProvider):
     def is_allowed(self, request: HttpRequest, total: Decimal=None):
         return 'pretix.plugins.manualpayment' in self.event.plugins and super().is_allowed(request, total)
 
-    def order_change_allowed(self, order: Order):
-        return 'pretix.plugins.manualpayment' in self.event.plugins and super().order_change_allowed(order)
+    def order_change_allowed(self, order: Order, request=None):
+        return 'pretix.plugins.manualpayment' in self.event.plugins and super().order_change_allowed(order, request)
 
     @property
     def public_name(self):
diff --git a/src/pretix/presale/views/user.py b/src/pretix/presale/views/user.py
index 7ff3f4638..b81457a1b 100644
--- a/src/pretix/presale/views/user.py
+++ b/src/pretix/presale/views/user.py
@@ -97,7 +97,8 @@ class UnlockHashView(EventViewMixin, View):
 
     def get(self, request, *args, **kwargs):
         hashes = request.session.get('pretix_unlock_hashes', [])
-        hashes.append(kwargs.get('hash'))
+        if kwargs.get('hash') not in hashes:
+            hashes.append(kwargs.get('hash'))
         request.session['pretix_unlock_hashes'] = hashes
 
         if 'voucher' in request.GET: