diff --git a/doc/src/sgml/ref/pgupgrade.sgml b/doc/src/sgml/ref/pgupgrade.sgml
new file mode 100644
index b99e546..3957241
*** a/doc/src/sgml/ref/pgupgrade.sgml
--- b/doc/src/sgml/ref/pgupgrade.sgml
***************
*** 61,67 ****
    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>
  
    <para>
--- 61,68 ----
    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</>.  Compatible collation
!   library versions must also be used.
   </para>
  
    <para>