diff --git a/wp-includes/pluggable.php b/wp-includes/pluggable.php
index 8a205cdfca..c64b99dca6 100644
--- a/wp-includes/pluggable.php
+++ b/wp-includes/pluggable.php
@@ -1167,7 +1167,7 @@ function wp_generate_password($length = 12) {
 	$chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()";
 	$password = '';
 	for ( $i = 0; $i < $length; $i++ )
-		$password .= substr($chars, mt_rand(0, strlen($chars)), 1);
+		$password .= substr($chars, mt_rand(0, strlen($chars) - 1), 1);
 	return $password;
 }
 endif;