diff --git a/TLSharp.Core/TelegramClient.cs b/TLSharp.Core/TelegramClient.cs
index 0692486..0a7b070 100644
--- a/TLSharp.Core/TelegramClient.cs
+++ b/TLSharp.Core/TelegramClient.cs
@@ -111,6 +111,9 @@ namespace TLSharp.Core
 
         private async Task RequestWithDcMigration(TLMethod request) 
         {
+            if (_sender == null)
+                throw new InvalidOperationException("Not connected!");
+
             var completed = false;
             while(!completed)
             {
@@ -139,9 +142,6 @@ namespace TLSharp.Core
             if (String.IsNullOrWhiteSpace(phoneNumber))
                 throw new ArgumentNullException(nameof(phoneNumber));
 
-            if (_sender == null)
-                throw new InvalidOperationException("Not connected!");
-
             var authCheckPhoneRequest = new TLRequestCheckPhone() { PhoneNumber = phoneNumber };
 
             await RequestWithDcMigration(authCheckPhoneRequest);