diff --git a/Lidgren.Network/NetPeer.Send.cs b/Lidgren.Network/NetPeer.Send.cs
index 7eab62d..664c4e0 100644
--- a/Lidgren.Network/NetPeer.Send.cs
+++ b/Lidgren.Network/NetPeer.Send.cs
@@ -62,6 +62,8 @@ namespace Lidgren.Network
 
 		internal int GetMTU(IList<NetConnection> recipients)
 		{
+			NetException.Assert(recipients.Count > 0);
+
 			int mtu = int.MaxValue;
 			foreach (NetConnection conn in recipients)
 			{
@@ -85,6 +87,8 @@ namespace Lidgren.Network
 				throw new ArgumentNullException("msg");
 			if (recipients == null)
 				throw new ArgumentNullException("recipients");
+			if (recipients.Count < 1)
+				throw new NetException("recipients must contain at least one item");
 			if (method == NetDeliveryMethod.Unreliable || method == NetDeliveryMethod.ReliableUnordered)
 				NetException.Assert(sequenceChannel == 0, "Delivery method " + method + " cannot use sequence channels other than 0!");
 			if (msg.m_isSent)
@@ -95,7 +99,7 @@ namespace Lidgren.Network
 			msg.m_isSent = true;
 
 			int len = msg.LengthBytes;
-			if (len <= m_configuration.MaximumTransmissionUnit)
+			if (len <= mtu)
 			{
 				Interlocked.Add(ref msg.m_recyclingCount, recipients.Count);
 				foreach (NetConnection conn in recipients)
@@ -176,6 +180,8 @@ namespace Lidgren.Network
 				throw new ArgumentNullException("msg");
 			if (recipients == null)
 				throw new ArgumentNullException("recipients");
+			if (recipients.Count < 1)
+				throw new NetException("recipients must contain at least one item");
 			if (msg.m_isSent)
 				throw new NetException("This message has already been sent! Use NetPeer.SendMessage() to send to multiple recipients efficiently");
 			if (msg.LengthBytes > m_configuration.MaximumTransmissionUnit)
diff --git a/Lidgren.Network/NetPeerConfiguration.cs b/Lidgren.Network/NetPeerConfiguration.cs
index 33f2784..c610d58 100644
--- a/Lidgren.Network/NetPeerConfiguration.cs
+++ b/Lidgren.Network/NetPeerConfiguration.cs
@@ -187,13 +187,15 @@ namespace Lidgren.Network
 		}
 
 		/// <summary>
-		/// Gets or sets the maximum amount of bytes to send in a single packet, excluding ip, udp and lidgren headers
+		/// Gets or sets the maximum amount of bytes to send in a single packet, excluding ip, udp and lidgren headers. Cannot be changed once NetPeer is initialized.
 		/// </summary>
 		public int MaximumTransmissionUnit
 		{
 			get { return m_maximumTransmissionUnit; }
 			set
 			{
+				if (m_isLocked)
+					throw new NetException(c_isLockedMessage);
 				if (value < 1 || value >= ((ushort.MaxValue + 1) / 8))
 					throw new NetException("MaximumTransmissionUnit must be between 1 and " + (((ushort.MaxValue + 1) / 8) - 1) + " bytes");
 				m_maximumTransmissionUnit = value;