diff --git a/man/os-release.xml b/man/os-release.xml
index 5a0cfd2887..a6d333f278 100644
--- a/man/os-release.xml
+++ b/man/os-release.xml
@@ -317,6 +317,23 @@
         </para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><varname>DEFAULT_HOSTNAME=</varname></term>
+
+        <listitem><para>A string specifying the hostname if
+        <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry> is not
+        present and no other configuration source specifies the hostname. Must be either a single DNS label
+        (a string composed of 7-bit ASCII lower-case characters and no spaces or dots, limited to the format
+        allowed for DNS domain name labels), or a sequence of such labels separated by single dots that forms
+        a valid DNS FQDN. The total length must be at most 64 characters.</para>
+
+        <para>See
+        <citerefentry><refentrytitle>org.freedesktop.hostname1</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for a description of how
+        <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+        determines the fallback hostname.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><varname>SYSEXT_LEVEL=</varname></term>