diff --git a/Controller/BackendController.php b/Controller/BackendController.php
index cf55435..ce9b8bb 100755
--- a/Controller/BackendController.php
+++ b/Controller/BackendController.php
@@ -94,7 +94,7 @@ final class BackendController extends Controller
     {
         /** @var \phpOMS\Model\Html\Head $head */
         $head = $response->get('Content')->getData('head');
-        $head->addAsset(AssetType::CSS, '/Modules/Calendar/Theme/Backend/css/styles.css');
+        $head->addAsset(AssetType::CSS, '/Modules/Calendar/Theme/Backend/css/styles.css?v=1.0.0');
 
         $view = new View($this->app->l11nManager, $request, $response);
         $view->setTemplate('/Modules/ProjectManagement/Theme/Backend/projectmanagement-profile');