diff --git a/share/man/man9/ieee80211_radiotap.9 b/share/man/man9/ieee80211_radiotap.9
index c6253e3296ea..cc8b9250bcc0 100644
--- a/share/man/man9/ieee80211_radiotap.9
+++ b/share/man/man9/ieee80211_radiotap.9
@@ -1,4 +1,4 @@
-.\" $NetBSD: ieee80211_radiotap.9,v 1.3 2005/04/25 14:37:49 wiz Exp $
+.\" $NetBSD: ieee80211_radiotap.9,v 1.4 2005/07/11 21:59:12 dyoung Exp $
 .\"
 .\" Copyright (c) 2004	Bruce M. Simpson <bms@spc.org>,
 .\"			Darron Broad <darron@kewl.org>,
@@ -186,7 +186,12 @@ arbitrary, fixed reference.
 This bit is reserved for any future extensions to the
 .Vt radiotap
 structure.
-It should not be used at this time.
+A driver sets IEEE80211_RADIOTAP_EXT to extend the it_present bitmap
+by another 64 bits.
+The bitmap can be extended by multiples of 32 bits to 96, 128, 160
+bits or longer, by setting IEEE80211_RADIOTAP_EXT in the extensions.
+The bitmap ends at the first extension field where IEEE80211_RADIOTAP_EXT
+is not set.
 .El
 .Sh EXAMPLES
 Radiotap header for the Cisco Aironet driver: