diff --git a/chapter07/createfiles.xml b/chapter07/createfiles.xml
index 7df2acde6..ca148f966 100644
--- a/chapter07/createfiles.xml
+++ b/chapter07/createfiles.xml
@@ -169,6 +169,15 @@ EOF</userinput></screen>
   freely by the system administrator since well-written programs do not depend
   on GID numbers, but rather use the group's name.</para>
 
+  <para>The ID 65534 is used by the kernel for NFS and separate user
+  namespaces for unmapped users (those exist on the NFS server or the parent
+  user namespace, but <quote>do not exist</quote> on the local machine or in
+  the separate namespace).  We assign
+  <systemitem class="username">nobody</systemitem> and
+  <systemitem class="groupname">nogroup</systemitem> for it to avoid an
+  unnamed ID.  But other distros may treat this ID differently, so any
+  portable program should not depend on this assignment.</para>
+
   <para>Some tests in <xref linkend="chapter-building-system"/> need a regular
   user. We add this user here and delete this account at the end of that
   chapter.</para>