diff --git a/README.md b/README.md
index cf98c11..1654243 100644
--- a/README.md
+++ b/README.md
@@ -23,3 +23,14 @@ Module allows integrate CMS Prestashop with [retailCRM](https://www.retailcrm.pr
 
 * This release contains an experimental feature "corporate customers". Use at your own risk.
 * This release only supports retailCRM API v5.
+
+#### Customization
+
+If you want to change the default behavior of a module classes and be sure that these changes won't be overwritten during the module upgrade process, you should **copy the original classes** that you are going to customize to the `prestashop-root/modules/retailcrm_custom/classes` directory. 
+
+From here you can modify the methods of the classes for your own purposes, and they will not be affected during the module upgrade process.
+
+Keep in mind that:
+
+* If the logic and classes of the module have changed a lot after an upgrade, your customized logic may cause the module to malfunction. **You should always check for changes after an upgrade and update your customized classes if needed.**
+* This feature does not allow to customize the base class (file `retailcrm.php`). For this you can use the standard Prestashop override feature.
diff --git a/retailcrm/bootstrap.php b/retailcrm/bootstrap.php
index d867b64..5c80da4 100644
--- a/retailcrm/bootstrap.php
+++ b/retailcrm/bootstrap.php
@@ -60,6 +60,12 @@ class RetailcrmAutoloader
      */
     protected static $pathTop;
 
+    /**
+     * The top level directory where recursion for custom classes will begin.
+     *
+     */
+    protected static $pathTopCustom;
+
     /**
      * Autoload function for registration with spl_autoload_register
      *
@@ -70,6 +76,21 @@ class RetailcrmAutoloader
      */
     public static function loader($className)
     {
+        if (file_exists(self::$pathTopCustom) && is_dir(self::$pathTopCustom)) {
+            $directory = new RecursiveDirectoryIterator(self::$pathTopCustom);
+            $fileIterator = new RecursiveIteratorIterator($directory);
+            $filename = $className . self::$fileExt;
+
+            foreach ($fileIterator as $file) {
+                if (Tools::strtolower($file->getFilename()) === Tools::strtolower($filename)
+                    && $file->isReadable()
+                    && !class_exists($className)
+                ) {
+                    include_once $file->getPathname();
+                }
+            }
+        }
+
         $directory = new RecursiveDirectoryIterator(self::$pathTop);
         $fileIterator = new RecursiveIteratorIterator($directory);
         $filename = $className . self::$fileExt;
@@ -104,8 +125,20 @@ class RetailcrmAutoloader
     {
         self::$pathTop = $path;
     }
+
+    /**
+     * Sets the $pathTopCustom property
+     *
+     * @param string $path The path representing the top level where recursion for custom
+     *                     classes should begin. Defaults to 'modules/retailcrm_custom/classes'.
+     */
+    public static function setPathCustom($path)
+    {
+        self::$pathTopCustom = $path;
+    }
 }
 
 RetailcrmAutoloader::setPath(realpath(dirname(__FILE__)));
+RetailcrmAutoloader::setPathCustom(realpath(_PS_MODULE_DIR_ . '/retailcrm_custom/classes'));
 RetailcrmAutoloader::setFileExt('.php');
 spl_autoload_register('RetailcrmAutoloader::loader');
diff --git a/retailcrm/lib/RetailcrmOrderBuilder.php b/retailcrm/lib/RetailcrmOrderBuilder.php
index 44ae657..af4a406 100644
--- a/retailcrm/lib/RetailcrmOrderBuilder.php
+++ b/retailcrm/lib/RetailcrmOrderBuilder.php
@@ -894,6 +894,8 @@ class RetailcrmOrderBuilder
             }
         }
 
+        $crmOrder['discountManualAmount'] = round($order->total_discounts, 2);
+
         if (isset($payment[$paymentType]) && !empty($payment[$paymentType])) {
             $order_payment = array(
                 'externalId' => $order->id . '#' . $order->reference,
@@ -901,8 +903,6 @@ class RetailcrmOrderBuilder
                 'type' => $payment[$paymentType]
             );
 
-            $crmOrder['discountManualAmount'] = round($order->total_discounts, 2);
-
             if (((float) $crmOrder['discountManualAmount']) > ((float) $order_payment['amount'])) {
                 $crmOrder['discountManualAmount'] = $order_payment['amount'];
             }