diff --git a/man/os-release.xml b/man/os-release.xml
index 674180679b..5a0cfd2887 100644
--- a/man/os-release.xml
+++ b/man/os-release.xml
@@ -317,6 +317,17 @@
         </para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><varname>SYSEXT_LEVEL=</varname></term>
+
+        <listitem><para>A lower-case string (mostly numeric, no spaces or other characters outside of 0–9,
+        a–z, ".", "_" and "-") identifying the operating system extensions support level, to indicate which
+        extension images are supported (See:
+        <citerefentry><refentrytitle>systemd-sysext</refentrytitle><manvolnum>8</manvolnum></citerefentry>).
+        Example: <literal>SYSEXT_LEVEL=2</literal> or
+        <literal>SYSEXT_LEVEL=15.14</literal>.</para></listitem>
+      </varlistentry>
+
     </variablelist>
 
     <para>If you are reading this file from C code or a shell script