diff --git a/doc/src/sgml/pgupgrade.sgml b/doc/src/sgml/pgupgrade.sgml
index 6d2cdaa335a2d985430c58290c65d845bd0fbe7c..9081cc916ae068534e8581e3ab75bbc77fff92b3 100644
--- a/doc/src/sgml/pgupgrade.sgml
+++ b/doc/src/sgml/pgupgrade.sgml
@@ -21,7 +21,8 @@
   regularly added to PostgreSQL major releases, the internal data storage
   format rarely changes.  <application>pg_upgrade</> does its best to
   make sure the old and new clusters are binary-compatible, e.g.  by
-  checking for compatible compile-time settings.  It is important that
+  checking for compatible compile-time settings, including 32/64-bit
+  binaries.  It is important that
   any external modules are also binary compatible, though this cannot
   be checked by <application>pg_upgrade</>.
  </para>