diff --git a/src/pretix/presale/checkoutflow.py b/src/pretix/presale/checkoutflow.py
index 803dc13e95..ada4464c6f 100644
--- a/src/pretix/presale/checkoutflow.py
+++ b/src/pretix/presale/checkoutflow.py
@@ -188,7 +188,7 @@ class AddOnsStep(CartMixin, AsyncAction, TemplateFlowStep):
         item_cache = {}
         for cartpos in get_cart(self.request).filter(addon_to__isnull=True).prefetch_related(
             'item__addons', 'item__addons__addon_category', 'addons', 'addons__variation',
-        ):
+        ).order_by('pk'):
             current_addon_products = {
                 a.item_id: a.variation_id for a in cartpos.addons.all()
             }