diff --git a/docs/MultiISP.xml b/docs/MultiISP.xml
index 0d3fc177e..3f3b86613 100644
--- a/docs/MultiISP.xml
+++ b/docs/MultiISP.xml
@@ -2585,8 +2585,9 @@ FALLBACK=
 PROXYDMZ=
 SQUID2=</programlisting>
 
-      <para>The last three variables are used to configure the firewall
-      differently to exercise various Shorewall features.</para>
+      <para>The last five variables are used to configure the firewall
+      differently to exercise various Shorewall features. Their use requires
+      Shorewall 4.5.2 or later.</para>
 
       <para>Here are the key entries in
       <filename>/etc/shorewall/shorewall.conf</filename>:</para>