diff --git a/doc/src/sgml/pgupgrade.sgml b/doc/src/sgml/pgupgrade.sgml
new file mode 100644
index 30f4544..3743599
*** a/doc/src/sgml/pgupgrade.sgml
--- b/doc/src/sgml/pgupgrade.sgml
*************** psql --username postgres --file script.s
*** 518,523 ****
--- 518,530 ----
    </para>
  
    <para>
+    While a Log-Shipping Standby Server (<xref linkend="warm-standby">) can
+    be upgraded, the server must be in changed to a primary server to allow
+    writes, and after the upgrade it cannot be reused as a standby server.
+    (Running <command>rsync</> after the upgrade allows reuse.)
+   </para>
+ 
+   <para>
     If you want to use link mode and you do not want your old cluster
     to be modified when the new cluster is started, make a copy of the
     old cluster and upgrade that in link mode. To make a valid copy