diff --git a/phpseclib/Common/Functions/Strings.php b/phpseclib/Common/Functions/Strings.php
index ef7500e6..72cca8a9 100644
--- a/phpseclib/Common/Functions/Strings.php
+++ b/phpseclib/Common/Functions/Strings.php
@@ -378,6 +378,11 @@ abstract class Strings
      */
     public static function increment_str(&$var)
     {
+        if (function_exists('sodium_increment')) {
+            sodium_increment($var);
+            return;
+        }
+
         for ($i = 4; $i <= strlen($var); $i+= 4) {
             $temp = substr($var, -$i, 4);
             switch ($temp) {