diff --git a/library/include/mobilisis/calculator_functions.h b/library/include/mobilisis/calculator_functions.h
index c592678..050e0c6 100644
--- a/library/include/mobilisis/calculator_functions.h
+++ b/library/include/mobilisis/calculator_functions.h
@@ -40,12 +40,12 @@ public:
     }
 
     void ResetTimeSteps(int paymentOptionIndex) {
-        if (m_timeSteps.size() > 0) {
+        if (m_timeSteps.size() > 0 && paymentOptionIndex < m_timeSteps.size()) {
             m_timeSteps[paymentOptionIndex].clear();
         }
     }
     QList<int> timeSteps(int paymentOptionIndex=0) const {
-        if (m_timeSteps.size() > 0) {
+        if (m_timeSteps.size() > 0 && paymentOptionIndex < m_timeSteps.size()) {
             return m_timeSteps[paymentOptionIndex];
         }
         return QList<int>();