diff --git a/TLSharp.Core/Network/MtProtoSender.cs b/TLSharp.Core/Network/MtProtoSender.cs
index 91e4457..5cbc9cf 100644
--- a/TLSharp.Core/Network/MtProtoSender.cs
+++ b/TLSharp.Core/Network/MtProtoSender.cs
@@ -34,7 +34,9 @@ namespace TLSharp.Core.Network
 
         private int GenerateSequence(bool confirmed)
         {
-            return confirmed ? session.Sequence++ * 2 + 1 : session.Sequence * 2;
+            lock (session.Lock) {
+                return confirmed ? session.Sequence++ * 2 + 1 : session.Sequence * 2;
+            }
         }
 
         public async Task Send(TeleSharp.TL.TLMethod request, CancellationToken token = default(CancellationToken))
diff --git a/TLSharp.Core/Session.cs b/TLSharp.Core/Session.cs
index 6a526cc..48b972b 100644
--- a/TLSharp.Core/Session.cs
+++ b/TLSharp.Core/Session.cs
@@ -72,6 +72,8 @@ namespace TLSharp.Core
 
     public class Session
     {
+        internal object Lock = new object ();
+
 	    private const string defaultConnectionAddress = "149.154.175.100";//"149.154.167.50";
 
 		private const int defaultConnectionPort = 443;