How to validate DocBook 5 with XInclude?

Is it possible to validate a DocBook 5 document which uses XInclude? I ask  
as I get an error for a simple document like this:

<?xml version="1.0" encoding="utf-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"  
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
xmlns:xi="http://www.w3.org/2001/XInclude"  
xsi:schemaLocation="http://docbook.org/ns/docbook  
http://www.docbook.org/xml/5.0/xsd/docbook.xsd" version="5.0">
   <title>Bar</title>
   <sect1>
     <title>Foo</title>
     <programlisting>
       <xi:include href="src.cpp" parse="text" />
     </programlisting>
   </sect1>
</chapter>

My validator complains that xi:include is an invalid child element of  
programlisting.

Boris