diff --git a/vendor/magento/module-advanced-checkout/Model/Cart.php b/vendor/magento/module-advanced-checkout/Model/Cart.php
index 9c0c031d9e4..2a0ae12a6a3 100644
--- a/vendor/magento/module-advanced-checkout/Model/Cart.php
+++ b/vendor/magento/module-advanced-checkout/Model/Cart.php
@@ -1242,7 +1242,7 @@ class Cart extends \Magento\Framework\DataObject implements \Magento\Checkout\Mo
         $checkedItems = $this->areProductsSalable($checkedItems);
         $products = $this->preloadProducts($checkedItems);
         foreach ($checkedItems as $sku => &$item) {
-            $itemProduct = $products[$sku] ?? null;
+            $itemProduct = $products[mb_strtolower($sku)] ?? null;
             $item = $this->checkItem(
                 $sku,
                 $item['qty'],
@@ -1934,13 +1934,15 @@ class Cart extends \Magento\Framework\DataObject implements \Magento\Checkout\Mo
             $collection->addAttributeToSelect('*');
             $collection->addFieldToFilter('sku', ['in' => $skuForFind]);
             $collection->setFlag('has_stock_status_filter', false);
+            $itemsLowerCase = array_combine(array_map('mb_strtolower', array_keys($items)), $items);
             foreach ($collection as $product) {
+                $sku = $product->getSku();
                 $isSalable = true;
-                if ($items[$product->getSku()]['code'] === Data::ADD_ITEM_STATUS_FAILED_OUT_OF_STOCK) {
+                if ($itemsLowerCase[mb_strtolower($sku)]['code'] === Data::ADD_ITEM_STATUS_FAILED_OUT_OF_STOCK) {
                     $isSalable = false;
                 }
                 $product->setIsSalable($isSalable);
-                $products[$product->getSku()] = $product;
+                $products[mb_strtolower($sku)] = $product;
                 $this->addProductToLocalCache($product, $product->getStoreId());
             }
         }