diff --git a/library/include/mobilisis/calculator_functions.h b/library/include/mobilisis/calculator_functions.h
index de40267..be42a1f 100644
--- a/library/include/mobilisis/calculator_functions.h
+++ b/library/include/mobilisis/calculator_functions.h
@@ -91,7 +91,7 @@ public:
     // helper function to find time steps for a tariff with PaymentMethod::Steps
     // (e.g. Schoenau/Koenigsee)
     //
-    QList<int> GetTimeSteps(Configuration *cfg, int paymentOptionIndex=0) const;
+    QList<int> &GetTimeSteps(Configuration *cfg, int paymentOptionIndex=0) const;
     QList<int> GetSteps(Configuration *cfg, int paymentOptionIndex=0) const { return GetTimeSteps(cfg, paymentOptionIndex); }
 
     QList<int> GetPriceSteps(Configuration *cfg) const;