From 41dd8b89d108ad01ef22583fd8314499f573b342 Mon Sep 17 00:00:00 2001
From: sta <sta.blockhead@gmail.com>
Date: Sat, 15 Aug 2020 22:30:33 +0900
Subject: [PATCH] [Modify] Polish it

---
 websocket-sharp/Net/HttpListenerPrefixCollection.cs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/websocket-sharp/Net/HttpListenerPrefixCollection.cs b/websocket-sharp/Net/HttpListenerPrefixCollection.cs
index e1215ac2..4c3e038d 100644
--- a/websocket-sharp/Net/HttpListenerPrefixCollection.cs
+++ b/websocket-sharp/Net/HttpListenerPrefixCollection.cs
@@ -134,13 +134,18 @@ namespace WebSocketSharp.Net
     public void Add (string uriPrefix)
     {
       _listener.CheckDisposed ();
+
       HttpListenerPrefix.CheckPrefix (uriPrefix);
+
       if (_prefixes.Contains (uriPrefix))
         return;
 
       _prefixes.Add (uriPrefix);
-      if (_listener.IsListening)
-        EndPointManager.AddPrefix (uriPrefix, _listener);
+
+      if (!_listener.IsListening)
+        return;
+
+      EndPointManager.AddPrefix (uriPrefix, _listener);
     }
 
     /// <summary>