diff --git a/man/os-release.xml b/man/os-release.xml
index fd98be5b7a..c5a53ae7eb 100644
--- a/man/os-release.xml
+++ b/man/os-release.xml
@@ -355,9 +355,12 @@
 
           <listitem><para>The date at which support for this version of the OS ends. (What exactly "lack of
           support" means varies between vendors, but generally users should assume that updates, including
-          security fixes, will not be provided.) The value is a date in the format
-          <literal>YYYY-MM-DD</literal>, and specifies the last day on which support <emphasis>is</emphasis>
-          provided.</para></listitem>
+          security fixes, will not be provided.) The value is a date in the ISO 8601 format
+          <literal>YYYY-MM-DD</literal>, and specifies the first day on which support <emphasis>is
+          not</emphasis> provided.</para>
+
+          <para>For example, <literal>SUPPORT_END=2001-01-01</literal> means that the system was supported
+          until the end of the last day of the previous millenium.</para></listitem>
         </varlistentry>
 
         <varlistentry>