diff --git a/websocket-sharp/Server/WebSocketSessionManager.cs b/websocket-sharp/Server/WebSocketSessionManager.cs
index fb4b670d..9863af5e 100644
--- a/websocket-sharp/Server/WebSocketSessionManager.cs
+++ b/websocket-sharp/Server/WebSocketSessionManager.cs
@@ -572,6 +572,7 @@ namespace WebSocketSharp.Server
     /// <exception cref="InvalidOperationException">
     /// The current state of the manager is not Start.
     /// </exception>
+    [Obsolete ("This method will be removed.")]
     public Dictionary<string, bool> Broadping ()
     {
       if (_state != ServerState.Start) {