diff --git a/doc/probackup.xml b/doc/probackup.xml
index c839cb26..8ea3cdc4 100644
--- a/doc/probackup.xml
+++ b/doc/probackup.xml
@@ -1,7 +1,7 @@
 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
           "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
 [
-<!ENTITY pgprobackup     SYSTEM "pgprobackup.sgml">
+<!ENTITY pgprobackup     SYSTEM "pgprobackup.xml">
 ]>
 
 <book id="pg-probackup">