diff --git a/websocket-sharp/Server/WebSocketSessionManager.cs b/websocket-sharp/Server/WebSocketSessionManager.cs
index c9526522..37fb37e4 100644
--- a/websocket-sharp/Server/WebSocketSessionManager.cs
+++ b/websocket-sharp/Server/WebSocketSessionManager.cs
@@ -895,12 +895,6 @@ namespace WebSocketSharp.Server
     ///   -or-
     ///   </para>
     ///   <para>
-    ///   The session could not be found.
-    ///   </para>
-    ///   <para>
-    ///   -or-
-    ///   </para>
-    ///   <para>
     ///   <paramref name="code"/> is 1010 (mandatory extension).
     ///   </para>
     ///   <para>
@@ -917,6 +911,9 @@ namespace WebSocketSharp.Server
     ///   <paramref name="reason"/> could not be UTF-8-encoded.
     ///   </para>
     /// </exception>
+    /// <exception cref="InvalidOperationException">
+    /// The session could not be found.
+    /// </exception>
     /// <exception cref="ArgumentOutOfRangeException">
     ///   <para>
     ///   <paramref name="code"/> is less than 1000 or greater than 4999.
@@ -933,7 +930,7 @@ namespace WebSocketSharp.Server
       IWebSocketSession session;
       if (!TryGetSession (id, out session)) {
         var msg = "The session could not be found.";
-        throw new ArgumentException (msg, "id");
+        throw new InvalidOperationException (msg);
       }
 
       session.Context.WebSocket.Close (code, reason);