diff --git a/Classes/EventListener/Order/Stock/ProcessOrderCheckStock.php b/Classes/EventListener/Order/Stock/ProcessOrderCheckStock.php
new file mode 100644
index 00000000..b0563840
--- /dev/null
+++ b/Classes/EventListener/Order/Stock/ProcessOrderCheckStock.php
@@ -0,0 +1,93 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Extcode\CartProducts\EventListener\Order\Stock;
+
+/*
+ * This file is part of the package extcode/cart-products.
+ *
+ * For the full copyright and license information, please read the
+ * LICENSE file that was distributed with this source code.
+ */
+
+use Extcode\Cart\Event\ProcessOrderCheckStockEvent;
+use Extcode\CartProducts\Domain\Model\Product\Product;
+use Extcode\CartProducts\Domain\Repository\Product\ProductRepository;
+use TYPO3\CMS\Core\Messaging\FlashMessage;
+use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;
+use TYPO3\CMS\Core\Utility\GeneralUtility;
+use TYPO3\CMS\Extbase\Utility\LocalizationUtility;
+
+class ProcessOrderCheckStock
+{
+    public function __construct(
+        protected readonly ProductRepository $productRepository
+    ) {
+    }
+
+    public function __invoke(ProcessOrderCheckStockEvent $event): void
+    {
+        $cart = $event->getCart();
+        $cartProducts = $cart->getProducts();
+
+        foreach ($cartProducts as $cartProduct) {
+            if ($cartProduct->getProductType() !== 'CartProducts') {
+                continue;
+            }
+
+            $querySettings = $this->productRepository->createQuery()->getQuerySettings();
+            $querySettings->setRespectStoragePage(false);
+            $this->productRepository->setDefaultQuerySettings($querySettings);
+            $product = $this->productRepository->findByIdentifier($cartProduct->getProductId());
+
+            if (!$product instanceof Product || !$product->isHandleStock()) {
+                continue;
+            }
+
+            $compareQuantity = $cartProduct->getQuantity();
+
+            if (!$product->isHandleStockInVariants()) {
+                $quantityInStock = $product->getStock();
+                if ($compareQuantity > $quantityInStock) {
+                    $this->falseAvailability($event, $product->getTitle(), $product->getSku(), $quantityInStock);
+                }
+                continue;
+            }
+
+            foreach ($product->getBeVariants() as $beVariant) {
+                foreach ($cartProduct->getBeVariants() as $cartBeVariant) {
+                    if($cartBeVariant->getSku() !== $beVariant->getSku()) {
+                        continue;
+                    }
+                    $quantityInStock = $beVariant->getStock();
+                    if ($compareQuantity > $quantityInStock) {
+                        $this->falseAvailability($event, $product->getTitle(), $beVariant->getSku(), $quantityInStock);
+                    }
+                }
+            }
+        }
+    }
+
+    protected function falseAvailability(
+        ProcessOrderCheckStockEvent $event,
+        string $title,
+        string $sku,
+        int $quantityInStock
+    ): void
+    {
+        $event->setNotEveryProductAvailable();
+        $event->addInsufficientStockMessage(
+            GeneralUtility::makeInstance(
+                FlashMessage::class,
+                LocalizationUtility::translate(
+                    'tx_cart.error.stock_handling.order',
+                    'cart',
+                    [$title, $sku, $quantityInStock]
+                ),
+                '',
+                ContextualFeedbackSeverity::ERROR
+            )
+        );
+    }
+}
diff --git a/Configuration/Services.yaml b/Configuration/Services.yaml
index 70f2448b..2060d0bd 100644
--- a/Configuration/Services.yaml
+++ b/Configuration/Services.yaml
@@ -66,6 +66,13 @@ services:
         identifier: 'cart-products--check-product-availability'
         event: Extcode\Cart\Event\CheckProductAvailabilityEvent
 
+  Extcode\CartProducts\EventListener\Order\Stock\ProcessOrderCheckStock:
+    tags:
+      - name: event.listener
+        identifier: 'cart-products--process-order-check-stock'
+        event: Extcode\Cart\Event\ProcessOrderCheckStockEvent
+
+
   Extcode\CartProducts\Reaction\UpdateStockReaction:
     tags: ['reactions.reaction']
     public: true
diff --git a/Documentation/Changelog/5.0/Feature-138-ListenToProcessOrderCheckStockEvent.rst b/Documentation/Changelog/5.0/Feature-138-ListenToProcessOrderCheckStockEvent.rst
new file mode 100644
index 00000000..5567ab6c
--- /dev/null
+++ b/Documentation/Changelog/5.0/Feature-138-ListenToProcessOrderCheckStockEvent.rst
@@ -0,0 +1,34 @@
+.. include:: ../../Includes.txt
+
+======================================================
+Breaking: #138 - Listen to ProcessOrderCheckStockEvent
+======================================================
+
+See :issue:`138`
+
+Description
+===========
+
+`EXT:cart` v9 will have an extended :php:`Extcode\Cart\Domain\Model\Cart\Cart\ProcessOrderCheckStockEvent`.
+This allows product extensions as `EXT:cart_product` to set a flag if any
+product of an order is not available in sufficient amount (means: less articles
+in stock than what a customer wants to order).
+
+The new Event Listener :php:`Extcode\CartProducts\EventListener\Order\Stock\ProcessOrderCheckStock`
+checks whether the stock of any article is lower than what a customer wants to
+order. This situation can happen when customer B ordered the same product
+after customer A put the article into the cart. Customer A will get in this case
+a message that the article is no longer available in the desired amount and the
+order can not be finished until customer A adapts the amount.
+
+Impact
+======
+
+Negative effects are not expected. This feature works out of the box when
+stock handling is activated. As long as flash messages are shown in the order
+form it's not necessary to adapt anything.
+
+It is of course possible to override the displayed message which has the key
+`tx_cart.error.stock_handling.order` (in EXT:cart).
+
+.. index:: Backend
diff --git a/Documentation/Changelog/5.0/Index.rst b/Documentation/Changelog/5.0/Index.rst
new file mode 100644
index 00000000..d4775fc4
--- /dev/null
+++ b/Documentation/Changelog/5.0/Index.rst
@@ -0,0 +1,30 @@
+.. include:: ../../Includes.txt
+
+5.0 Changes
+===========
+
+**Table of contents**
+
+.. contents::
+   :local:
+   :depth: 1
+
+Breaking Changes
+^^^^^^^^^^^^^^^^
+
+.. toctree::
+   :maxdepth: 1
+   :titlesonly:
+   :glob:
+
+   Breaking-*
+
+Features
+^^^^^^^^
+
+.. toctree::
+   :maxdepth: 1
+   :titlesonly:
+   :glob:
+
+   Feature-*
diff --git a/Documentation/Changelog/Index.rst b/Documentation/Changelog/Index.rst
index deee5fa0..da592ad2 100644
--- a/Documentation/Changelog/Index.rst
+++ b/Documentation/Changelog/Index.rst
@@ -7,6 +7,7 @@ ChangeLog
    :maxdepth: 5
    :titlesonly:
 
+   5.0/Index
    4.0/Index
    3.0/Index
    2.4/Index