diff --git a/vendor/magento/module-inventory-quote-graph-ql/Model/Cart/MergeCarts/CartQuantityValidator.php b/vendor/magento/module-inventory-quote-graph-ql/Model/Cart/MergeCarts/CartQuantityValidator.php
index 635106ae87cb..13b3f17f62a7 100644
--- a/vendor/magento/module-inventory-quote-graph-ql/Model/Cart/MergeCarts/CartQuantityValidator.php
+++ b/vendor/magento/module-inventory-quote-graph-ql/Model/Cart/MergeCarts/CartQuantityValidator.php
@@ -12,6 +12,7 @@
 use Magento\Quote\Api\CartItemRepositoryInterface;
 use Magento\Quote\Api\Data\CartInterface;
 use Magento\Quote\Api\Data\CartItemInterface;
+use Magento\Quote\Model\Quote\Item;
 use Magento\QuoteGraphQl\Model\Cart\MergeCarts\CartQuantityValidatorInterface;
 use Magento\InventorySalesApi\Api\GetProductSalableQtyInterface;
 use Magento\InventoryCatalog\Model\GetStockIdForCurrentWebsite;
@@ -33,6 +34,11 @@ class CartQuantityValidator implements CartQuantityValidatorInterface
      */
     private $getStockIdForCurrentWebsite;
 
+    /**
+     * @var array
+     */
+    private $cumulativeQty = [];
+
     /**
      * @param CartItemRepositoryInterface $cartItemRepository
      * @param GetProductSalableQtyInterface $getProductSalableQty
@@ -59,13 +65,22 @@ public function validateFinalCartQuantities(CartInterface $customerCart, CartInt
     {
         $modified = false;
         $stockId = $this->getStockIdForCurrentWebsite->execute();
+        $this->cumulativeQty = [];
+
         /** @var CartItemInterface $guestCartItem */
         foreach ($guestCart->getAllVisibleItems() as $guestCartItem) {
             foreach ($customerCart->getAllItems() as $customerCartItem) {
                 if ($customerCartItem->compare($guestCartItem)) {
-                    $product = $customerCartItem->getProduct();
-                    $productSalableQty = $this->getProductSalableQty->execute($product->getSku(), $stockId);
-                    if ($productSalableQty < $guestCartItem->getQty() + $customerCartItem->getQty()) {
+                    $enoughQty = $customerCartItem->getChildren()
+                        ? $this->validateCompositeProductQty($stockId, $guestCartItem, $customerCartItem)
+                        : $this->validateProductQty(
+                            $stockId,
+                            $customerCartItem->getProduct()->getSku(),
+                            $guestCartItem->getQty(),
+                            $customerCartItem->getQty()
+                        );
+
+                    if (!$enoughQty) {
                         try {
                             $this->cartItemRepository->deleteById($guestCart->getId(), $guestCartItem->getItemId());
                             $modified = true;
@@ -78,6 +93,65 @@ public function validateFinalCartQuantities(CartInterface $customerCart, CartInt
                 }
             }
         }
+        $this->cumulativeQty = [];
+
         return $modified;
     }
+
+    /**
+     * Validate product stock availability
+     *
+     * @param int $stockId
+     * @param string $sku
+     * @param float $guestItemQty
+     * @param float $customerItemQty
+     * @return bool
+     */
+    private function validateProductQty(int $stockId, string $sku, float $guestItemQty, float $customerItemQty): bool
+    {
+        $salableQty = $this->getProductSalableQty->execute($sku, $stockId);
+        $this->cumulativeQty[$sku] ??= 0;
+        $this->cumulativeQty[$sku] += $guestItemQty + $customerItemQty;
+
+        return $salableQty >= $this->cumulativeQty[$sku];
+    }
+
+    /**
+     * Validate composite product stock availability
+     *
+     * @param int $stockId
+     * @param Item $guestCartItem
+     * @param Item $customerCartItem
+     * @return bool
+     */
+    private function validateCompositeProductQty(int $stockId, Item $guestCartItem, Item $customerCartItem): bool
+    {
+        $guestChildItems = $this->retrieveChildItems($guestCartItem);
+        foreach ($customerCartItem->getChildren() as $customerChildItem) {
+            $sku = $customerChildItem->getProduct()->getSku();
+            $customerItemQty = $customerCartItem->getQty() * $customerChildItem->getQty();
+            $guestItemQty = $guestCartItem->getQty() * $guestChildItems[$sku]->getQty();
+            if (!$this->validateProductQty($stockId, $sku, $guestItemQty, $customerItemQty)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Retrieve child quote items mapped by sku
+     *
+     * @param Item $quoteItem
+     * @return array
+     */
+    private function retrieveChildItems(Item $quoteItem): array
+    {
+        $childItems = [];
+        foreach ($quoteItem->getChildren() as $childItem) {
+            $childItems[$childItem->getProduct()->getSku()] = $childItem;
+        }
+
+        return $childItems;
+    }
 }