Index: modules/in-commerce/units/orders/orders_event_handler.php
===================================================================
--- modules/in-commerce/units/orders/orders_event_handler.php
+++ modules/in-commerce/units/orders/orders_event_handler.php
@@ -2271,21 +2271,18 @@
 	}
 
 	/**
-	 * Set next available order number
+	 * Set next available order number.
 	 *
-	 * @param kEvent $event
+	 * @param kEvent $event Event.
+	 *
+	 * @return void
 	 */
-	function setNextOrderNumber($event)
+	protected function setNextOrderNumber(kEvent $event)
 	{
+		/** @var OrdersItem $object */
 		$object = $event->getObject();
-		/* @var $object OrdersItem */
-
-		$sql = 'SELECT MAX(Number)
-				FROM ' . $this->Application->GetLiveName($object->TableName);
-		$next_order_number = $this->Conn->GetOne($sql) + 1;
 
-		$next_order_number = max($next_order_number, $this->Application->ConfigValue('Comm_Next_Order_Number'));
-		$this->Application->SetConfigValue('Comm_Next_Order_Number', $next_order_number + 1);
+		$next_order_number = $this->getNextOrderNumber();
 
 		$object->SetDBField('Number', $next_order_number);
 		$object->SetDBField('SubNumber', 0);
@@ -2299,6 +2296,50 @@
 	}
 
 	/**
+	 * Returns order number to be used next.
+	 *
+	 * @return integer
+	 */
+	protected function getNextOrderNumber()
+	{
+		$lock_clause = array(
+			TABLE_PREFIX . 'IdGenerator WRITE',
+			$this->Application->getUnitOption('conf', 'TableName') . ' WRITE',
+			$this->Application->getUnitOption($this->Prefix, 'TableName') . ' WRITE',
+		);
+		$this->Conn->Query('LOCK TABLES ' . implode(', ', $lock_clause));
+
+		$sql = 'UPDATE ' . $this->Application->getUnitOption('conf', 'TableName') . '
+				SET VariableValue = GREATEST(VariableValue, ' . $this->getLastUsedOrderNumber() . ') + 1
+				WHERE VariableName = "Comm_Next_Order_Number"';
+		$this->Conn->Query($sql);
+
+		$sql = 'SELECT VariableValue
+				FROM ' . $this->Application->getUnitOption('conf', 'TableName') . '
+				WHERE VariableName = "Comm_Next_Order_Number"';
+		$next_order_number = $this->Conn->GetOne($sql);
+
+		$this->Application->SetConfigValue('Comm_Next_Order_Number', $next_order_number);
+
+		$this->Conn->Query('UNLOCK TABLES');
+
+		return $next_order_number - 1;
+	}
+
+	/**
+	 * Returns last used order number.
+	 *
+	 * @return integer
+	 */
+	protected function getLastUsedOrderNumber()
+	{
+		$sql = 'SELECT MAX(Number)
+				FROM ' . $this->Application->getUnitOption($this->Prefix, 'TableName');
+
+		return (int)$this->Conn->GetOne($sql);
+	}
+
+	/**
 	 * Set's new order address based on another address from order (e.g. billing from shipping)
 	 *
 	 * @param unknown_type $object