diff --git a/src/Illuminate/Support/Str.php b/src/Illuminate/Support/Str.php
index 50c73bf2a1b9..8b23bfad5edb 100644
--- a/src/Illuminate/Support/Str.php
+++ b/src/Illuminate/Support/Str.php
@@ -1125,11 +1125,12 @@ public static function studly($value)
      * @param  string  $string
      * @param  int  $start
      * @param  int|null  $length
+     * @param  string  $encoding
      * @return string
      */
-    public static function substr($string, $start, $length = null)
+    public static function substr($string, $start, $length = null, $encoding = 'UTF-8')
     {
-        return mb_substr($string, $start, $length, 'UTF-8');
+        return mb_substr($string, $start, $length, $encoding);
     }
 
     /**