diff --git a/app/Jobs/ScheduledJobManager.php b/app/Jobs/ScheduledJobManager.php
index 4c3beb97cd..c218a53652 100644
--- a/app/Jobs/ScheduledJobManager.php
+++ b/app/Jobs/ScheduledJobManager.php
@@ -64,15 +64,23 @@ class ScheduledJobManager implements ShouldQueue
 
     private int $skippedCount = 0;
 
+    /**
+     * One key of TYPES, or null for all types.
+     *
+     * Declared with a default instead of promoted, so jobs queued by older versions without this property still run.
+     */
+    public ?string $type = null;
+
     /**
      * @param  string|null  $type  One key of TYPES, or null for all types.
      */
-    public function __construct(public ?string $type = null)
+    public function __construct(?string $type = null)
     {
         if ($type !== null && ! array_key_exists($type, self::TYPES)) {
             throw new \InvalidArgumentException("Unknown scheduled job type [{$type}].");
         }
 
+        $this->type = $type;
         $this->onQueue(crons_queue());
     }
 
diff --git a/tests/Unit/ScheduledJobManagerLegacyPayloadTest.php b/tests/Unit/ScheduledJobManagerLegacyPayloadTest.php
new file mode 100644
index 0000000000..4aa846c684
--- /dev/null
+++ b/tests/Unit/ScheduledJobManagerLegacyPayloadTest.php
@@ -0,0 +1,18 @@
+<?php
+
+use App\Jobs\ScheduledJobManager;
+use Illuminate\Queue\Middleware\WithoutOverlapping;
+use Tests\TestCase;
+
+uses(TestCase::class);
+
+it('uses the shared lock for a job queued before scheduled job types existed', function () {
+    // v4.3.23 serialized ScheduledJobManager without a type property.
+    $job = unserialize('O:'.strlen(ScheduledJobManager::class).':"'.ScheduledJobManager::class.'":0:{}');
+
+    $middleware = $job->middleware();
+
+    expect($job->type)->toBeNull()
+        ->and($middleware[0])->toBeInstanceOf(WithoutOverlapping::class)
+        ->and($middleware[0]->key)->toBe('scheduled-job-manager');
+});