diff --git a/library/include/mobilisis/calculate_price.h b/library/include/mobilisis/calculate_price.h
index 0681c73..e9ecd19 100644
--- a/library/include/mobilisis/calculate_price.h
+++ b/library/include/mobilisis/calculate_price.h
@@ -174,7 +174,8 @@ CalcState CALCULATE_LIBRARY_API compute_price_for_parking_ticket(
                                             QDateTime &start_parking_time,
                                             int netto_parking_time,
                                             QDateTime &end_parking_time,    // return value
-                                            struct price_t *price);         // return value
+                                            struct price_t *price,          // return value
+                                            bool prepaid = true);
 
 CalcState CALCULATE_LIBRARY_API compute_duration_for_parking_ticket(        // deprecated
                                             parking_tariff_t *tariff,