diff --git a/websocket-sharp/Ext.cs b/websocket-sharp/Ext.cs
index ff85a42cf..9df2373bd 100644
--- a/websocket-sharp/Ext.cs
+++ b/websocket-sharp/Ext.cs
@@ -506,7 +506,7 @@ internal static bool IsData (this Opcode opcode)
 
     internal static bool IsPortNumber (this int value)
     {
-      return value > 0 && value < 65536;
+      return value > -1 && value < 65536;
     }
 
     internal static bool IsReserved (this ushort code)
diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index 9657da323..7b3613111 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -123,7 +123,7 @@ public WebSocketServer ()
     /// on which to listen.
     /// </param>
     /// <exception cref="ArgumentOutOfRangeException">
-    /// <paramref name="port"/> is less than 1 or greater than 65535.
+    /// <paramref name="port"/> is less than 0 or greater than 65535.
     /// </exception>
     public WebSocketServer (int port)
       : this (port, port == 443)
@@ -213,12 +213,12 @@ public WebSocketServer (string url)
     /// secure connections; otherwise, <c>false</c>.
     /// </param>
     /// <exception cref="ArgumentOutOfRangeException">
-    /// <paramref name="port"/> is less than 1 or greater than 65535.
+    /// <paramref name="port"/> is less than 0 or greater than 65535.
     /// </exception>
     public WebSocketServer (int port, bool secure)
     {
       if (!port.IsPortNumber ()) {
-        var msg = "Less than 1 or greater than 65535.";
+        var msg = "Less than 0 or greater than 65535.";
         throw new ArgumentOutOfRangeException ("port", msg);
       }
 
@@ -965,6 +965,11 @@ private void startReceiving ()
       _receiveThread = new Thread (new ThreadStart (receiveRequest));
       _receiveThread.IsBackground = true;
       _receiveThread.Start ();
+      
+      if (_port == 0)
+      {
+          _port = ((System.Net.IPEndPoint)_listener.LocalEndpoint).Port;
+      }
     }
 
     private void stop (ushort code, string reason)