diff --git a/src/Service/Rtt/RttRecoveryComputationService.php b/src/Service/Rtt/RttRecoveryComputationService.php
index c40044a..19b8c1d 100644
--- a/src/Service/Rtt/RttRecoveryComputationService.php
+++ b/src/Service/Rtt/RttRecoveryComputationService.php
@@ -254,7 +254,8 @@ final readonly class RttRecoveryComputationService
                 }
 
                 $contractAtSolidarity = $employeeContractsByDate[$solidarityDate] ?? null;
-                $solidarityIsoDay     = (int) new DateTimeImmutable($solidarityDate)->format('N');
+                // Le Lundi de Pentecôte est toujours un lundi (ISO 1), mais on le dérive pour rester explicite.
+                $solidarityIsoDay = (int) new DateTimeImmutable($solidarityDate)->format('N');
                 // Attendu RÉEL du jour (planning workDaysHours), pas la répartition uniforme :
                 // c'est ce qui rend la neutralisation correcte (cf. spec).
                 $solidarityExpected = $this->dailyReferenceResolver->resolve(
diff --git a/tests/Service/Rtt/RttRecoveryComputationServiceTest.php b/tests/Service/Rtt/RttRecoveryComputationServiceTest.php
index 09232b9..b6c9630 100644
--- a/tests/Service/Rtt/RttRecoveryComputationServiceTest.php
+++ b/tests/Service/Rtt/RttRecoveryComputationServiceTest.php
@@ -209,6 +209,8 @@ final class RttRecoveryComputationServiceTest extends TestCase
 
     /**
      * CUSTOM 28h : prorata = round(28×12) = 336 (5h36). worked 0, expected 336 → delta 0.
+     * Le delta est nul ici par coïncidence du fallback uniforme (expected = prorata) ; avec un vrai
+     * workDaysHours où la valeur du lundi diffère, expected ≠ prorata et le delta serait non nul.
      */
     public function testSolidarityAdjustmentCustom28hUsesProrata(): void
     {