diff --git a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpChannelListener.cs b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpChannelListener.cs
index 10672f9beaa0c06d31dfe94bbb23013fb13e930a..77c0463f46763ea4950402fa013a599e2a12d58a 100644
--- a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpChannelListener.cs
+++ b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpChannelListener.cs
@@ -98,6 +98,8 @@ namespace System.ServiceModel.Discovery.Udp
 			if (!accept_wait_handle.WaitOne (timeout))
 				throw new TimeoutException ();
 			accept_wait_handle.Reset ();
+			if (State != CommunicationState.Opened)
+				return null; // happens during Close() or Abort().
 			channel = new UdpDuplexChannel (this);
 			channel.Closed += delegate {
 				accept_wait_handle.Set ();
diff --git a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpDuplexChannel.cs b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpDuplexChannel.cs
index 48ef6b65018e8ea2d50514fff99aafb7f0fc2f48..4a97e904709e148a696c83f8d83cb7b3f0902196 100644
--- a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpDuplexChannel.cs
+++ b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery.Udp/UdpDuplexChannel.cs
@@ -252,7 +252,6 @@ if (result == null) throw new ArgumentNullException ("result");
 				if (isMulticast) {
 					multicast_address = ip;
 					client = new UdpClient (new IPEndPoint (IPAddress.Any, port));
-					client.ExclusiveAddressUse = false;
 					client.JoinMulticastGroup (ip, binding_element.TransportSettings.TimeToLive);
 				}
 				else