diff --git a/src/Service/Cart/Voucher/VoucherCartCollector.php b/src/Service/Cart/Voucher/VoucherCartCollector.php
index ddba643dc..2d7819a43 100644
--- a/src/Service/Cart/Voucher/VoucherCartCollector.php
+++ b/src/Service/Cart/Voucher/VoucherCartCollector.php
@@ -72,7 +72,7 @@ public function collect(CartDataCollection $data, Cart $original, SalesChannelCo
         $cartHasVoucher = false;
 
         if ($salesChannelHasVoucherMethod) {
-            foreach ($original->getLineItems() as $item) {
+            foreach ($original->getLineItems()->getFlat() as $item) {
                 # get the final inherited voucher type of the product
                 # this might even be from the parent
                 $voucherType = $this->voucherService->getFinalVoucherType($item, $context);