diff --git a/TLSharp.Core/TelegramClient.cs b/TLSharp.Core/TelegramClient.cs
index 2fa8c3a..85561ad 100644
--- a/TLSharp.Core/TelegramClient.cs
+++ b/TLSharp.Core/TelegramClient.cs
@@ -99,6 +99,9 @@ namespace TLSharp.Core
 
         public async Task<bool> IsPhoneRegisteredAsync(string phoneNumber)
         {
+            if (String.IsNullOrWhiteSpace(phoneNumber))
+                throw new ArgumentNullException(nameof(phoneNumber));
+
             if (_sender == null)
                 throw new InvalidOperationException("Not connected!");
 
@@ -111,6 +114,9 @@ namespace TLSharp.Core
 
         public async Task<string> SendCodeRequestAsync(string phoneNumber)
         {
+            if (String.IsNullOrWhiteSpace(phoneNumber))
+                throw new ArgumentNullException(nameof(phoneNumber));
+
             var completed = false;
 
             TLRequestSendCode request = null;
@@ -136,6 +142,15 @@ namespace TLSharp.Core
 
         public async Task<TLUser> MakeAuthAsync(string phoneNumber, string phoneCodeHash, string code)
         {
+            if (String.IsNullOrWhiteSpace(phoneNumber))
+                throw new ArgumentNullException(nameof(phoneNumber));
+
+            if (String.IsNullOrWhiteSpace(phoneCodeHash))
+                throw new ArgumentNullException(nameof(phoneCodeHash));
+
+            if (String.IsNullOrWhiteSpace(code))
+                throw new ArgumentNullException(nameof(code));
+
             var request = new TLRequestSignIn() { phone_number = phoneNumber, phone_code_hash = phoneCodeHash, phone_code = code };
             await _sender.Send(request);
             await _sender.Receive(request);