diff --git a/library/include/mobilisis/calculate_price.h b/library/include/mobilisis/calculate_price.h
index ab09de4..8df9da2 100644
--- a/library/include/mobilisis/calculate_price.h
+++ b/library/include/mobilisis/calculate_price.h
@@ -111,6 +111,9 @@ int CALCULATE_LIBRARY_API get_zone_nr(int zone = -1);
 
 int CALCULATE_LIBRARY_API compute_next_timestep(parking_tariff_t *tariff, int currentTimeMinutes, int UpDown);
 
+class Calculator;
+Calculator CALCULATE_LIBRARY_API *get_calculator();
+
 CalcState CALCULATE_LIBRARY_API compute_price_for_parking_ticket(       // deprecated
                                             parking_tariff_t *tariff,
                                             time_t start_parking_time,