diff --git a/Modbus.Net/Modbus.Net/Controller/BaseController.cs b/Modbus.Net/Modbus.Net/Controller/BaseController.cs
index e33b5ff..c2491bc 100644
--- a/Modbus.Net/Modbus.Net/Controller/BaseController.cs
+++ b/Modbus.Net/Modbus.Net/Controller/BaseController.cs
@@ -76,7 +76,7 @@ namespace Modbus.Net
         /// <inheritdoc />
         public virtual void SendStart()
         {
-            if (SendingThread == null)
+            if (!IsSending)
             {
                 SendingThread = Task.Run(() => SendingMessageControlInner());
             }