diff --git a/src/aircraft.h b/src/aircraft.h
--- a/src/aircraft.h
+++ b/src/aircraft.h
@@ -139,5 +139,6 @@ struct Aircraft FINAL : public Specializ
 void GetRotorImage(const Aircraft *v, EngineImageType image_type, VehicleSpriteSeq *result);
 
 Station *GetTargetAirportIfValid(const Aircraft *v);
+void HandleMissingAircraftOrders(Aircraft *v);
 
 #endif /* AIRCRAFT_H */