diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index 19a9953b..1f969edf 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -552,15 +552,12 @@ namespace WebSocketSharp.Server
       }
 
       set {
-        string msg;
-        if (!canSet (out msg)) {
-          _log.Warn (msg);
-          return;
-        }
-
         lock (_sync) {
+          string msg;
+
           if (!canSet (out msg)) {
             _log.Warn (msg);
+
             return;
           }