diff --git a/composer.json b/composer.json
index eff5f00..59e5d25 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,8 @@
     "require": {
         "php": ">=5.4.0",
         "illuminate/support": "4.*",
-        "illuminate/container": "4.*"
+        "illuminate/container": "4.*",
+        "ext-mbstring": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "3.7.*",
diff --git a/src/Filter/Filter.php b/src/Filter/Filter.php
index a1297ec..fd72a18 100644
--- a/src/Filter/Filter.php
+++ b/src/Filter/Filter.php
@@ -181,19 +181,42 @@ public function registerDefaultFilters()
 		});
 
         $this->registerFilter('upper', function($value, array $args) {
-            return strtoupper($value);
+            return mb_strtoupper($value);
         });
 
         $this->registerFilter('lower', function($value, array $args) {
-            return strtolower($value);
+            return mb_strtolower($value);
         });
 
         $this->registerFilter('capfirst', function($value, array $args) {
-            return ucfirst($value);
+            return $this->mb_ucfirst($value);
         });
 
         $this->registerFilter('lowerfirst', function($value, array $args) {
-            return lcfirst($value);
+            return $this->mb_lcfirst($value);
         });
     }
+
+    /**
+     * @param $string
+     * @param string $encoding
+     * @return string
+     */
+    protected function mb_ucfirst($string, $encoding = 'UTF-8')
+    {
+        $firstChar = mb_substr($string, 0, 1, $encoding);
+        $then = mb_substr($string, 1, null, $encoding);
+        return mb_strtoupper($firstChar, $encoding) . $then;
+    }
+
+    /**
+     * @param $string
+     * @return string
+     */
+    protected function mb_lcfirst($string, $encoding = 'UTF-8')
+    {
+        $firstChar = mb_substr($string, 0, 1, $encoding);
+        $then = mb_substr($string, 1, null, $encoding);
+        return mb_strtolower($firstChar, $encoding) . $then;
+    }
 }
\ No newline at end of file