diff --git a/Source/MQTTnet/Client/Options/MqttClientCertificateValidationEventArgs.cs b/Source/MQTTnet/Client/Options/MqttClientCertificateValidationEventArgs.cs
index f1842cb1e..ff4825612 100644
--- a/Source/MQTTnet/Client/Options/MqttClientCertificateValidationEventArgs.cs
+++ b/Source/MQTTnet/Client/Options/MqttClientCertificateValidationEventArgs.cs
@@ -14,8 +14,14 @@ public sealed class MqttClientCertificateValidationEventArgs : EventArgs
 
         public X509Chain Chain { get; set; }
 
-        public SslPolicyErrors SslPolicyErrors { get; set; }
-
         public IMqttClientChannelOptions ClientOptions { get; set; }
+#if NET452 || NET461 || NET48
+        /// <summary>
+        ///     Can be a host string name or an object derived from WebRequest.
+        /// </summary>
+        public object Sender { get; set; }
+#endif
+
+        public SslPolicyErrors SslPolicyErrors { get; set; }
     }
-}
+}
\ No newline at end of file
diff --git a/Source/MQTTnet/Implementations/MqttWebSocketChannel.cs b/Source/MQTTnet/Implementations/MqttWebSocketChannel.cs
index b75688c82..be31c2a51 100644
--- a/Source/MQTTnet/Implementations/MqttWebSocketChannel.cs
+++ b/Source/MQTTnet/Implementations/MqttWebSocketChannel.cs
@@ -249,9 +249,11 @@ void SetupClientWebSocket(ClientWebSocket clientWebSocket)
 #elif WINDOWS_UWP
                 throw new NotSupportedException("Remote certificate validation callback is not supported when using 'uap10.0'.");
 #elif NET452 || NET461 || NET48
-                ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => {
+                ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => 
+                {
                     var context = new MqttClientCertificateValidationEventArgs
                     {
+                        Sender = sender,
                         Certificate = certificate,
                         Chain = chain,
                         SslPolicyErrors = sslPolicyErrors,