diff --git a/framework/yii/helpers/base/StringHelper.php b/framework/yii/helpers/base/StringHelper.php
index 5b854ac..5134bf6 100644
--- a/framework/yii/helpers/base/StringHelper.php
+++ b/framework/yii/helpers/base/StringHelper.php
@@ -18,20 +18,18 @@ class StringHelper
 {
 	/**
 	 * Returns the number of bytes in the given string.
-	 * This method ensures the string is treated as a byte array.
-	 * It will use `mb_strlen()` if it is available.
+	 * This method ensures the string is treated as a byte array by using `mb_strlen()`.
 	 * @param string $string the string being measured for length
 	 * @return integer the number of bytes in the given string.
 	 */
 	public static function strlen($string)
 	{
-		return function_exists('mb_strlen') ? mb_strlen($string, '8bit') : strlen($string);
+		return mb_strlen($string, '8bit');
 	}
 
 	/**
 	 * Returns the portion of string specified by the start and length parameters.
-	 * This method ensures the string is treated as a byte array.
-	 * It will use `mb_substr()` if it is available.
+	 * This method ensures the string is treated as a byte array by using `mb_substr()`.
 	 * @param string $string the input string. Must be one character or longer.
 	 * @param integer $start the starting position
 	 * @param integer $length the desired portion length
@@ -40,15 +38,14 @@ class StringHelper
 	 */
 	public static function substr($string, $start, $length)
 	{
-		return function_exists('mb_substr') ? mb_substr($string, $start, $length, '8bit') : substr($string, $start, $length);
+		return mb_substr($string, $start, $length, '8bit');
 	}
 
 	/**
 	 * Returns the trailing name component of a path.
 	 * This method does the same as the php function basename() except that it will
 	 * always use \ and / as directory separators, independent of the operating system.
-	 * Note: basename() operates naively on the input string, and is not aware of the
-	 * actual filesystem, or path components such as "..".
+	 * Note: this method is not aware of the actual filesystem, or path components such as "..".
 	 * @param string $path A path string.
 	 * @param string $suffix If the name component ends in suffix this will also be cut off.
 	 * @return string the trailing name component of the given path.