diff --git a/websocket-sharp/Server/WebSocketBehavior.cs b/websocket-sharp/Server/WebSocketBehavior.cs
index af113e45..d054eed3 100644
--- a/websocket-sharp/Server/WebSocketBehavior.cs
+++ b/websocket-sharp/Server/WebSocketBehavior.cs
@@ -1225,7 +1225,7 @@ namespace WebSocketSharp.Server
     protected void Send (string data)
     {
       if (_websocket == null) {
-        var msg = "The session has not started yet.";
+        var msg = "The Send method is not available.";
 
         throw new InvalidOperationException (msg);
       }