diff --git a/inc/inc.ClassUtilities.php b/inc/inc.ClassUtilities.php
index eeb853c62..f90a5069c 100644
--- a/inc/inc.ClassUtilities.php
+++ b/inc/inc.ClassUtilities.php
@@ -50,9 +50,10 @@ class Utilities { /* {{{ */
 	 * @return string random string
 	 */
 	static public function makeRandomString($n, $alph = "0123456789abcdefghijklmnopqrstuvwxyz") { /* {{{ */
+		$len = strlen($alph)-1;
 		$s = "";
 		for ($i = 0; $i != $n; ++$i)
-			$s .= $alph[mt_rand(0, 35)];
+			$s .= $alph[mt_rand(0, $len)];
 		return $s;
 	} /* }}} */