diff --git a/src/Service/WorkHours/NightHoursCalculator.php b/src/Service/WorkHours/NightHoursCalculator.php
index a32104c..fe53ef6 100644
--- a/src/Service/WorkHours/NightHoursCalculator.php
+++ b/src/Service/WorkHours/NightHoursCalculator.php
@@ -13,7 +13,7 @@ use App\Entity\WorkHour;
  * (21:00-24:00). On projette sur J+1 pour les shifts qui traversent minuit.
  * Source de verite unique partagee par les ecrans Heures et les exports.
  */
-final class NightHoursCalculator
+final readonly class NightHoursCalculator
 {
     /**
      * Minutes de nuit d'un WorkHour. Conducteurs : champ manuel nightHoursMinutes.
diff --git a/tests/Service/WorkHours/NightHoursCalculatorTest.php b/tests/Service/WorkHours/NightHoursCalculatorTest.php
index ea0e554..08d6191 100644
--- a/tests/Service/WorkHours/NightHoursCalculatorTest.php
+++ b/tests/Service/WorkHours/NightHoursCalculatorTest.php
@@ -19,6 +19,7 @@ final class NightHoursCalculatorTest extends TestCase
         $calc = new NightHoursCalculator();
         self::assertSame(0, $calc->nightIntervalMinutes(null, null));
         self::assertSame(0, $calc->nightIntervalMinutes('08:00', null));
+        self::assertSame(0, $calc->nightIntervalMinutes(null, '17:00'));
     }
 
     public function testPureDayRangeHasNoNight(): void
@@ -28,6 +29,15 @@ final class NightHoursCalculatorTest extends TestCase
         self::assertSame(0, $calc->nightIntervalMinutes('08:00', '17:00'));
     }
 
+    public function testWindowBoundariesAreRightExclusive(): void
+    {
+        $calc = new NightHoursCalculator();
+        // 06:00 -> 21:00 : pile entre les deux fenetres de nuit, 0 min.
+        self::assertSame(0, $calc->nightIntervalMinutes('06:00', '21:00'));
+        // 22:00 -> 06:00 : 22-24 (120) + 00-06 (360) = 480, borne 06:00 exclue.
+        self::assertSame(480, $calc->nightIntervalMinutes('22:00', '06:00'));
+    }
+
     public function testEveningWindowCounts(): void
     {
         $calc = new NightHoursCalculator();