diff --git a/Blimp/mode.h b/Blimp/mode.h
index 8718d47fa1..59256771f6 100644
--- a/Blimp/mode.h
+++ b/Blimp/mode.h
@@ -18,6 +18,7 @@ public:
         VELOCITY =      2,  // velocity mode
         LOITER =        3,  // loiter mode (position hold)
         RTL =           4,  // rtl
+        // Mode number 30 reserved for "offboard" for external/lua control.
     };
 
     // constructor