diff --git a/websocket-sharp/HttpRequest.cs b/websocket-sharp/HttpRequest.cs
index 41f700e2..cfced5c8 100644
--- a/websocket-sharp/HttpRequest.cs
+++ b/websocket-sharp/HttpRequest.cs
@@ -133,7 +133,12 @@ namespace WebSocketSharp
       var headers = req.Headers;
       headers["Upgrade"] = "websocket";
       headers["Connection"] = "Upgrade";
-      headers["Host"] = uri.Port == 80 ? uri.DnsSafeHost : uri.Authority;
+      var port = uri.Port;
+      var scheme = uri.Scheme;
+      bool isDefaultPort = (port == 80 && scheme == "ws") || (port == 443 && scheme == "wss");
+      // only include port in host header if it is non-default
+      // https://tools.ietf.org/html/rfc6455#page-17
+      headers["Host"] = isDefaultPort ? uri.DnsSafeHost : uri.Authority;
 
       return req;
     }