diff --git a/Rover/mode.h b/Rover/mode.h
index 6b7b579702..87fb32bbfd 100644
--- a/Rover/mode.h
+++ b/Rover/mode.h
@@ -28,6 +28,7 @@ public:
         SMART_RTL    = 12,
         GUIDED       = 15,
         INITIALISING = 16,
+        // Mode number 30 reserved for "offboard" for external/lua control.
     };
 
     // Constructor