diff --git a/man/systemd-halt.service.xml b/man/systemd-halt.service.xml
index 2fd7b8bf80..0737d058d1 100644
--- a/man/systemd-halt.service.xml
+++ b/man/systemd-halt.service.xml
@@ -83,6 +83,12 @@
                 remaining swap devices, detach all remaining storage
                 devices and kill all remaining processes.</para>
 
+                <para>It is necessary to have this code in a separate binary
+                because otherwise rebooting after an upgrade might be broken —
+                the running PID 1 could still depend on libraries which are not
+                available any more, thus keeping the filesystem busy, which
+                then cannot be re-mounted read-only.</para>
+
                 <para>Immediately before executing the actual system
                 halt/poweroff/reboot/kexec
                 <filename>systemd-shutdown</filename> will run all