diff --git a/README.md b/README.md
index f773225..0f7add0 100644
--- a/README.md
+++ b/README.md
@@ -33,7 +33,7 @@ StringTools::camelize($str, $from) : string
 #### ::startsWith
 
 ```php
-StringTools::startsWith($str, $start, $encoding) : bool
+StringTools::startsWith($str, $start) : bool
 ```
 
 * `$str` string input
diff --git a/StringTools.php b/StringTools.php
index 679f6ca..c52d7c8 100644
--- a/StringTools.php
+++ b/StringTools.php
@@ -21,14 +21,13 @@ public static function camelize($str, $from = '_')
     /**
      * @param string $str
      * @param string $start
-     * @param string $encoding
      * @return bool
      */
-    public static function startsWith($str, $start, $encoding = 'UTF-8')
+    public static function startsWith($str, $start)
     {
-        $length = mb_strlen($start, $encoding);
+        $length = strlen($start);
 
-        return mb_substr($str, 0, $length, $encoding) === $start;
+        return substr($str, 0, $length) === $start;
     }
 
     /**