diff --git a/phpBB/includes/functions_user.php b/phpBB/includes/functions_user.php
index 9e136cc1ff..495f0dcacb 100644
--- a/phpBB/includes/functions_user.php
+++ b/phpBB/includes/functions_user.php
@@ -1473,6 +1473,7 @@ function user_ipwhois($ip)
 	if (($fsk = @fsockopen($whois_host, 43)))
 	{
 		// CRLF as per RFC3912
+		// Z to limit the query to all possible flags (whois.arin.net)
 		fputs($fsk, "z $ip\r\n");
 		while (!feof($fsk))
 		{