diff --git a/man/systemd-tmpfiles.xml b/man/systemd-tmpfiles.xml
index a6246844cb..735f59cc11 100644
--- a/man/systemd-tmpfiles.xml
+++ b/man/systemd-tmpfiles.xml
@@ -144,8 +144,10 @@
 
       <varlistentry>
         <term><option>--boot</option></term>
-        <listitem><para>Also execute lines with an exclamation mark.
-        </para></listitem>
+        <listitem><para>Also execute lines with an exclamation mark. Lines that are not safe to be executed
+        on a running system may be marked in this way. <command>systemd-tmpfiles</command> is executed in
+        early boot with <option>--boot</option> specified and will execute those lines. When invoked again
+        later, it should be called without <option>--boot</option>.</para></listitem>
       </varlistentry>
 
       <varlistentry>