diff --git a/man7/ip.7 b/man7/ip.7
index a7a0b4ecd..4cb3a9ae9 100644
--- a/man7/ip.7
+++ b/man7/ip.7
@@ -6,7 +6,7 @@
 .\" and in case of nontrivial modification author and date
 .\" of the modification is added to the header.
 .\" $Id: ip.7,v 1.19 2000/12/20 18:10:31 ak Exp $
-.TH IP  7 2008-08-08 "Linux" "Linux Programmer's Manual"
+.TH IP  7 2008-10-28 "Linux" "Linux Programmer's Manual"
 .SH NAME
 ip \- Linux IPv4 protocol implementation
 .SH SYNOPSIS
@@ -648,7 +648,12 @@ struct ip_mreqn {
 .I imr_multiaddr
 contains the address of the multicast group the application
 wants to join or leave.
-It must be a valid multicast address.
+It must be a valid multicast address
+.\" (i.e., within the 224.0.0.0-239.255.255.255 range)
+(or
+.BR setsockopt (2)
+fails with the error
+.BR EINVAL ).
 .I imr_address
 is the address of the local interface with which the system
 should join the multicast