diff --git a/classes/order/Order.php b/classes/order/Order.php
index 0b6597257..e57bf651d 100644
--- a/classes/order/Order.php
+++ b/classes/order/Order.php
@@ -1109,6 +1109,18 @@ class OrderCore extends ObjectModel
 		return Db::getInstance()->execute($sql);
 	}
 
+	public function getInvoiceNumber($order_invoice_id)
+	{
+		if (!$order_invoice_id)
+			return false;
+
+		return Db::getInstance()->getValue('
+			SELECT `number`
+			FROM `'._DB_PREFIX_.'order_invoice`
+			WHERE `id_order_invoice` = '.(int)$order_invoice_id
+		);
+	}
+
 	/**
 	 * This method allows to generate first invoice of the current order
 	 */
@@ -1193,11 +1205,46 @@ class OrderCore extends ObjectModel
 
 			// Keep it for backward compatibility, to remove on 1.6 version
 			$this->invoice_date = $order_invoice->date_add;
-			$this->invoice_number = $order_invoice->number;
+			$this->invoice_number = $this->getInvoiceNumber($order_invoice->id);
 			$this->update();
 		}
 	}
 
+	public function setDeliveryNumber($order_invoice_id, $id_shop)
+	{
+		if (!$order_invoice_id)
+			return false;
+
+		$number = Configuration::get('PS_DELIVERY_NUMBER', null, null, $id_shop);
+		// If invoice start number has been set, you clean the value of this configuration
+		if ($number)
+			Configuration::updateValue('PS_DELIVERY_NUMBER', false, false, null, $id_shop);
+
+		$sql = 'UPDATE `'._DB_PREFIX_.'order_invoice` SET delivery_number =';
+
+		if ($number)
+			$sql .= (int)$number;
+		else
+			$sql .= '(SELECT new_number FROM (SELECT (MAX(`delivery_number`) + 1) AS new_number
+			FROM `'._DB_PREFIX_.'order_invoice`) AS result)';
+
+		$sql .=' WHERE `id_order_invoice` = '.(int)$order_invoice_id;
+
+		return Db::getInstance()->execute($sql);
+	}
+
+	public function getDeliveryNumber($order_invoice_id)
+	{
+		if (!$order_invoice_id)
+			return false;
+
+		return Db::getInstance()->getValue('
+			SELECT `delivery_number`
+			FROM `'._DB_PREFIX_.'order_invoice`
+			WHERE `id_order_invoice` = '.(int)$order_invoice_id
+		);
+	}
+
 	public function setDelivery()
 	{
 		// Get all invoice
@@ -1206,24 +1253,14 @@ class OrderCore extends ObjectModel
 		{
 			if ($order_invoice->delivery_number)
 				continue;
-
-			$number = (int)Configuration::get('PS_DELIVERY_NUMBER', null, null, $this->id_shop);
-			if (!$number)
-			{
-				//if delivery number is not set or wrong, we set a default one.
-				Configuration::updateValue('PS_DELIVERY_NUMBER', 1, false, null, $this->id_shop);
-				$number = 1;
-			}
 				
 			// Set delivery number on invoice
-			$order_invoice->delivery_number = $number;
+			$order_invoice->delivery_number = 0;
 			$order_invoice->delivery_date = date('Y-m-d H:i:s');
 			// Update Order Invoice
 			$order_invoice->update();
-
-			// Keep for backward compatibility
-			$this->delivery_number = $number;
-			Configuration::updateValue('PS_DELIVERY_NUMBER', $number + 1, false, null, $this->id_shop);
+			$this->setDeliveryNumber($order_invoice->id, $this->id_shop);
+			$this->delivery_number = $this->getDeliveryNumber($order_invoice->id);
 		}
 
 		// Keep it for backward compatibility, to remove on 1.6 version