diff --git a/modbus_cli/modbus_tcp.py b/modbus_cli/modbus_tcp.py
index 4d9724f..0709435 100644
--- a/modbus_cli/modbus_tcp.py
+++ b/modbus_cli/modbus_tcp.py
@@ -9,7 +9,7 @@ class ModbusTcp:
     def __init__(self, host, port, slave_id, timeout):
         self.host = host
         self.port = port
-        if not slave_id:
+        if slave_id is None:
             slave_id = 255
         self.slave_id = slave_id
         self.timeout = timeout