diff --git a/dronecan/driver/__init__.py b/dronecan/driver/__init__.py
index 59b669c..07f38ec 100644
--- a/dronecan/driver/__init__.py
+++ b/dronecan/driver/__init__.py
@@ -32,7 +32,8 @@ def is_mavlink_port(device_name, **kwargs):
     if not have_mavcan:
         return False
     baudrate = kwargs.get('baudrate', 115200)
-    return MAVCAN.is_mavlink_port(device_name, baudrate)
+    source_system = kwargs.get('mavlink_source_system', 250)
+    return MAVCAN.is_mavlink_port(device_name, baudrate, source_system)
 
 def make_driver(device_name, **kwargs):
     """Creates an instance of CAN driver.
diff --git a/dronecan/driver/mavcan.py b/dronecan/driver/mavcan.py
index 4f0b9bf..0f6ba0a 100644
--- a/dronecan/driver/mavcan.py
+++ b/dronecan/driver/mavcan.py
@@ -34,7 +34,7 @@ def __init__(self, command, data):
         self.command = command
         self.data = data
 
-def io_process(url, bus, target_system, baudrate, tx_queue, rx_queue, exit_queue, parent_pid):
+def io_process(url, bus, source_system, target_system, baudrate, tx_queue, rx_queue, exit_queue, parent_pid):
     os.environ['MAVLINK20'] = '1'
 
     target_component = 0
@@ -47,8 +47,8 @@ def io_process(url, bus, target_system, baudrate, tx_queue, rx_queue, exit_queue
     readonly = False
 
     def connect():
-        nonlocal conn, baudrate, readonly
-        conn = mavutil.mavlink_connection(url, baud=baudrate, source_system=250,
+        nonlocal conn, baudrate, readonly, source_system
+        conn = mavutil.mavlink_connection(url, baud=baudrate, source_system=source_system,
                                           source_component=mavutil.mavlink.MAV_COMP_ID_MAVCAN,
                                           dialect='ardupilotmega')
         if conn is None:
@@ -203,6 +203,7 @@ def __init__(self, url, **kwargs):
         super(MAVCAN, self).__init__()
         self.bus = kwargs.get('bus_number', 1) - 1
         self.target_system = kwargs.get('mavlink_target_system', 0)
+        self.source_system = kwargs.get('mavlink_source_system', 250)
         self.filter_list = None
         baudrate = kwargs.get('baudrate', 115200)
 
@@ -211,7 +212,7 @@ def __init__(self, url, **kwargs):
         self.exit_queue = multiprocessing.Queue(maxsize=1)
 
         self.proc = multiprocessing.Process(target=io_process, name='mavcan_io_process',
-                                            args=(url, self.bus, self.target_system, baudrate,
+                                            args=(url, self.bus, self.source_system, self.target_system, baudrate,
                                             self.tx_queue, self.rx_queue, self.exit_queue, os.getpid()))
         self.proc.daemon = True
         self.proc.start()
@@ -248,10 +249,10 @@ def send_frame(self, frame):
         self._tx_hook(frame)
         self.tx_queue.put_nowait(frame)
 
-    def is_mavlink_port(device_name, baudrate):
+    def is_mavlink_port(device_name, baudrate, source_system):
         '''check if a device is sending mavlink'''
         os.environ['MAVLINK20'] = '1'
-        conn = mavutil.mavlink_connection(device_name, baud=baudrate, source_system=250, source_component=mavutil.mavlink.MAV_COMP_ID_MAVCAN)
+        conn = mavutil.mavlink_connection(device_name, baud=baudrate, source_system=source_system, source_component=mavutil.mavlink.MAV_COMP_ID_MAVCAN)
         if not conn:
             return False
         m = conn.recv_match(blocking=True, type=['HEARTBEAT','ATTITUDE', 'SYS_STATUS'], timeout=1.1)