diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index bc13cf55cd..83e08a9d9a 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -125,6 +125,7 @@ function set_config($config_name, $config_value, $is_dynamic = false)
 function gen_rand_string($num_chars = 8)
 {
 	$rand_str = unique_id();
+	$rand_str = str_replace('0', 'Z', strtoupper(base_convert($rand_str, 16, 35)));
 
 	return substr($rand_str, 0, $num_chars);
 }