diff --git a/mavutil.py b/mavutil.py
index 1aa9c2550..a8ae5237d 100644
--- a/mavutil.py
+++ b/mavutil.py
@@ -356,6 +356,10 @@ def probably_vehicle_heartbeat(self, msg):
                         mavlink.MAV_TYPE_ADSB,
                         mavlink.MAV_TYPE_ONBOARD_CONTROLLER):
             return False
+        if msg.autopilot in frozenset([
+                mavlink.MAV_AUTOPILOT_INVALID
+                ]):
+            return False
         return True
 
     def post_message(self, msg):