diff --git a/DataGrid/QueryHandler/DoctrineQueryHandler.php b/DataGrid/QueryHandler/DoctrineQueryHandler.php
index 0f2c52b..bc16040 100644
--- a/DataGrid/QueryHandler/DoctrineQueryHandler.php
+++ b/DataGrid/QueryHandler/DoctrineQueryHandler.php
@@ -78,7 +78,7 @@ public function transformValueCase(string $value): string
         if ($this->queryConfig->isCaseSensitive()) {
             return $value;
         } else {
-            return strtolower($value);
+            return mb_strtolower($value, 'UTF-8');
         }
     }
 
diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 6e2bfbc..bc1dbcb 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -17,8 +17,7 @@ class Configuration implements ConfigurationInterface
      */
     public function getConfigTreeBuilder()
     {
-        $treeBuilder = new TreeBuilder();
-        $rootNode = $treeBuilder->root('bilendi_dev_express');
+        $treeBuilder = new TreeBuilder('bilendi_dev_express');
 
         // Here you should define the parameters that are allowed to
         // configure your bundle. See the documentation linked above for
diff --git a/composer.json b/composer.json
index 025e8a1..84e2e6a 100644
--- a/composer.json
+++ b/composer.json
@@ -23,7 +23,8 @@
         "php": "^7.0",
         "doctrine/orm": "^2.5",
         "lstrojny/functional-php": "^1.4",
-        "symfony/framework-bundle": "^2.6|^3.2|^4.4"
+        "symfony/framework-bundle": "^2.6|^3.2|^4.4",
+        "ext-mbstring": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "^5.7",