diff --git a/src/Service/ParticipantEligibilityService.php b/src/Service/ParticipantEligibilityService.php
index 2ea785c..dbd28f0 100644
--- a/src/Service/ParticipantEligibilityService.php
+++ b/src/Service/ParticipantEligibilityService.php
@@ -92,7 +92,7 @@ class ParticipantEligibilityService
 
         $travelStartDate = CarbonImmutable::instance($bookingDto->travel->dateFrom);
         $birthDate = CarbonImmutable::instance($participant->dateOfBirth);
-        $ageAtTravelStart = $birthDate->diffInYears($travelStartDate);
+        $ageAtTravelStart = (int) $birthDate->diffInYears($travelStartDate);
         $birthYear = (int) $birthDate->format('Y');
 
         $constraintType = $service->ageConstraintType ?? 'absolute_age';