diff --git a/man7/arp.7 b/man7/arp.7
index 81012bfac..731378307 100644
--- a/man7/arp.7
+++ b/man7/arp.7
@@ -168,6 +168,14 @@ for at least a random value between
 An entry's validity will be extended if it receives positive feedback
 from higher level protocols.
 Defaults to 30 seconds.
+This file is now obsolete in favour of
+.IR base_reachable_time_ms .
+.TP
+.IR base_reachable_time_ms " (since Linux 2.6.12)"
+As for
+.IR base_reachable_time ,
+but measures time in millieseconds.
+Defaults to 30000 milliseconds.
 .TP
 .IR delay_first_probe_time " (since Linux 2.2)"
 .\" Precisely: 2.1.79