diff --git a/src/net/udpsock.go b/src/net/udpsock.go
index ec2bcfa607..571e099abd 100644
--- a/src/net/udpsock.go
+++ b/src/net/udpsock.go
@@ -259,6 +259,9 @@ func ListenUDP(network string, laddr *UDPAddr) (*UDPConn, error) {
 // ListenMulticastUDP is just for convenience of simple, small
 // applications. There are golang.org/x/net/ipv4 and
 // golang.org/x/net/ipv6 packages for general purpose uses.
+//
+// Note that ListenMulticastUDP will set the IP_MULTICAST_LOOP socket option
+// to 0 under IPPROTO_IP, to disable loopback of multicast packets.
 func ListenMulticastUDP(network string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, error) {
 	switch network {
 	case "udp", "udp4", "udp6":