diff --git a/library/src/calculate_price.cpp b/library/src/calculate_price.cpp
index e8f0731..2d3f4a5 100644
--- a/library/src/calculate_price.cpp
+++ b/library/src/calculate_price.cpp
@@ -35,6 +35,8 @@ CalcState CALCULATE_LIBRARY_API init_tariff(parking_tariff_t **tariff, char cons
     qCritical() << "      ... zone = " << zone;
 
     if (zone <= 0) {
+        delete *tariff;
+        *tariff = nullptr;
         return calcState.set(CalcState::State::ERROR_PARSING_ZONE_NR);
     }
 
@@ -59,9 +61,13 @@ CalcState CALCULATE_LIBRARY_API init_tariff(parking_tariff_t **tariff, char cons
 
         QString json = fname.readAll();
         if (! (*tariff)->ParseJson(*tariff, json.toStdString().c_str())) {
+            delete *tariff;
+            *tariff = nullptr;
             return calcState.set(CalcState::State::ERROR_PARSING_TARIFF);
         }
     } else {
+        delete *tariff;
+        *tariff = nullptr;
         return calcState.set(CalcState::State::ERROR_LOADING_TARIFF);
     }
 
@@ -71,7 +77,9 @@ CalcState CALCULATE_LIBRARY_API init_tariff(parking_tariff_t **tariff, char cons
 }
 
 void CALCULATE_LIBRARY_API free_tariff(parking_tariff_t *tariff) {
-    delete tariff;
+    if (tariff != nullptr) {
+        delete tariff;
+    }
 }
 
 CalcState CALCULATE_LIBRARY_API compute_price_for_parking_ticket(