diff --git a/src/BusProNet/Model/Booking.php b/src/BusProNet/Model/Booking.php
index 3f908e0..a9ea3dd 100644
--- a/src/BusProNet/Model/Booking.php
+++ b/src/BusProNet/Model/Booking.php
@@ -249,7 +249,7 @@ class Booking
         foreach ([...$this->transportationServices, ...$this->additionalServices] as $service) {
             if ((in_array($participantIndex, $service->mapping) || true === $service->mandatory)
                 && isset($service->individualPrice[$participantIndex])) {
-                $price += $service->individualPrice[$participantIndex];
+                $price += $service->individualPrice[$participantIndex] ?? 0;
             }
         }
 
@@ -257,13 +257,13 @@ class Booking
         foreach ($this->surcharges as $surcharge) {
             if (in_array($participantIndex, $surcharge->mapping)
                 && isset($surcharge->individualPrice[$participantIndex])) {
-                $price += $surcharge->individualPrice[$participantIndex];
+                $price += $surcharge->individualPrice[$participantIndex] ?? 0;
             }
         }
 
         $room = $this->getRoomForParticipant($participantIndex);
         if (null !== $room && isset($room->individualPrice[$participantIndex])) {
-            $price += $room->individualPrice[$participantIndex];
+            $price += $room->individualPrice[$participantIndex] ?? 0;
         }
 
         return $price;