diff --git a/websocket-sharp/Net/HttpListener.cs b/websocket-sharp/Net/HttpListener.cs
index 822b9d01..5d89368a 100644
--- a/websocket-sharp/Net/HttpListener.cs
+++ b/websocket-sharp/Net/HttpListener.cs
@@ -483,17 +483,19 @@ namespace WebSocketSharp.Net
 
     private void sendServiceUnavailable ()
     {
+      HttpListenerContext[] ctxs = null;
       lock (_ctxQueueSync) {
         if (_ctxQueue.Count == 0)
           return;
 
-        var ctxs = _ctxQueue.ToArray ();
+        ctxs = _ctxQueue.ToArray ();
         _ctxQueue.Clear ();
-        foreach (var ctx in ctxs) {
-          var res = ctx.Response;
-          res.StatusCode = (int) HttpStatusCode.ServiceUnavailable;
-          res.Close ();
-        }
+      }
+
+      foreach (var ctx in ctxs) {
+        var res = ctx.Response;
+        res.StatusCode = (int) HttpStatusCode.ServiceUnavailable;
+        res.Close ();
       }
     }