diff --git a/app/Services/BackupScheduling/BackupScheduleDispatcher.php b/app/Services/BackupScheduling/BackupScheduleDispatcher.php
index f0bd207..a9280cf 100644
--- a/app/Services/BackupScheduling/BackupScheduleDispatcher.php
+++ b/app/Services/BackupScheduling/BackupScheduleDispatcher.php
@@ -8,8 +8,9 @@
 use App\Models\Tenant;
 use App\Services\Intune\AuditLogger;
 use Carbon\CarbonImmutable;
-use Illuminate\Database\QueryException;
+use Illuminate\Database\UniqueConstraintViolationException;
 use Illuminate\Support\Facades\Bus;
+use Illuminate\Support\Facades\Log;
 
 class BackupScheduleDispatcher
 {
@@ -71,10 +72,20 @@ public function dispatchDue(?array $tenantIdentifiers = null): array
                     'status' => BackupScheduleRun::STATUS_RUNNING,
                     'summary' => null,
                 ]);
-            } catch (QueryException $exception) {
+            } catch (UniqueConstraintViolationException) {
                 // Idempotency: unique (backup_schedule_id, scheduled_for)
                 $skippedRuns++;
 
+                Log::debug('Backup schedule run already dispatched for slot.', [
+                    'tenant_id' => $schedule->tenant_id,
+                    'backup_schedule_id' => $schedule->id,
+                    'scheduled_for' => $slot->toDateTimeString(),
+                ]);
+
+                $schedule->forceFill([
+                    'next_run_at' => $this->scheduleTimeService->nextRunFor($schedule, $nowUtc),
+                ])->saveQuietly();
+
                 continue;
             }
 
diff --git a/specs/032-backup-scheduling-mvp/tasks.md b/specs/032-backup-scheduling-mvp/tasks.md
index 7a4403f..ee1571c 100644
--- a/specs/032-backup-scheduling-mvp/tasks.md
+++ b/specs/032-backup-scheduling-mvp/tasks.md
@@ -89,6 +89,7 @@ ### Tests (Pest)
 - [X] T038 [P] [US1] Add feature test tests/Feature/BackupScheduling/BackupScheduleBulkDeleteTest.php (bulk delete action regression)
 - [X] T039 [P] [US1] Extend tests/Feature/BackupScheduling/BackupScheduleBulkDeleteTest.php (operator cannot bulk delete)
 - [X] T041 [P] [US3] Make manual dispatch actions idempotent under concurrency in app/Filament/Resources/BackupScheduleResource.php (avoid unique constraint 500); add regression in tests/Feature/BackupScheduling/RunNowRetryActionsTest.php
+- [X] T042 [P] [US2] Harden dispatcher idempotency in app/Services/BackupScheduling/BackupScheduleDispatcher.php (catch unique constraint only; treat as already dispatched, no side effects) and extend tests/Feature/BackupScheduling/DispatchIdempotencyTest.php
 
 ### Implementation
 
diff --git a/tests/Feature/BackupScheduling/DispatchIdempotencyTest.php b/tests/Feature/BackupScheduling/DispatchIdempotencyTest.php
index 8ab996b..8df6cd6 100644
--- a/tests/Feature/BackupScheduling/DispatchIdempotencyTest.php
+++ b/tests/Feature/BackupScheduling/DispatchIdempotencyTest.php
@@ -38,3 +38,44 @@
 
     Bus::assertDispatchedTimes(RunBackupScheduleJob::class, 1);
 });
+
+it('treats a unique constraint collision as already-dispatched and advances next_run_at', function () {
+    CarbonImmutable::setTestNow(CarbonImmutable::create(2026, 1, 5, 10, 0, 30, 'UTC'));
+
+    [$user, $tenant] = createUserWithTenant(role: 'owner');
+    $this->actingAs($user);
+
+    $schedule = BackupSchedule::query()->create([
+        'tenant_id' => $tenant->id,
+        'name' => 'Daily 10:00',
+        'is_enabled' => true,
+        'timezone' => 'UTC',
+        'frequency' => 'daily',
+        'time_of_day' => '10:00:00',
+        'days_of_week' => null,
+        'policy_types' => ['deviceConfiguration'],
+        'include_foundations' => true,
+        'retention_keep_last' => 30,
+        'next_run_at' => null,
+    ]);
+
+    BackupScheduleRun::query()->create([
+        'backup_schedule_id' => $schedule->id,
+        'tenant_id' => $tenant->id,
+        'scheduled_for' => CarbonImmutable::now('UTC')->startOfMinute()->toDateTimeString(),
+        'status' => BackupScheduleRun::STATUS_RUNNING,
+        'summary' => null,
+    ]);
+
+    Bus::fake();
+
+    $dispatcher = app(BackupScheduleDispatcher::class);
+    $dispatcher->dispatchDue([$tenant->external_id]);
+
+    expect(BackupScheduleRun::query()->count())->toBe(1);
+    Bus::assertNotDispatched(RunBackupScheduleJob::class);
+
+    $schedule->refresh();
+    expect($schedule->next_run_at)->not->toBeNull();
+    expect($schedule->next_run_at->toDateTimeString())->toBe('2026-01-06 10:00:00');
+});