diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index db4c73d0..60071761 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -870,16 +870,6 @@ namespace WebSocketSharp.Server
 
     private void start (ServerSslConfiguration sslConfig)
     {
-      if (_state == ServerState.Start) {
-        _log.Info ("The server has already started.");
-        return;
-      }
-
-      if (_state == ServerState.ShuttingDown) {
-        _log.Warn ("The server is shutting down.");
-        return;
-      }
-
       lock (_sync) {
         if (_state == ServerState.Start) {
           _log.Info ("The server has already started.");
@@ -1292,6 +1282,18 @@ namespace WebSocketSharp.Server
     /// </exception>
     public void Start ()
     {
+      if (_state == ServerState.Start) {
+        _log.Info ("The server has already started.");
+
+        return;
+      }
+
+      if (_state == ServerState.ShuttingDown) {
+        _log.Warn ("The server is shutting down.");
+
+        return;
+      }
+
       ServerSslConfiguration sslConfig = null;
 
       if (_secure) {