diff --git a/apps/notifications/announcement_worker.py b/apps/notifications/announcement_worker.py
index 6724dd7..83d7132 100644
--- a/apps/notifications/announcement_worker.py
+++ b/apps/notifications/announcement_worker.py
@@ -94,7 +94,8 @@ def process_due_announcements(*, job_id=None):
     ).update(status=AnnouncementJob.Status.PENDING, next_attempt_at=now)
     with transaction.atomic():
         queryset = (
-            AnnouncementJob.objects.select_for_update(skip_locked=True)
+            # Nullable message/ticket joins must not be included in FOR UPDATE on PostgreSQL.
+            AnnouncementJob.objects.select_for_update(skip_locked=True, of=("self",))
             .filter(status=AnnouncementJob.Status.PENDING, next_attempt_at__lte=now)
             .select_related("message__ticket__customer", "ticket__customer")
             .annotate(priority=Case(When(source=AnnouncementJob.Source.MANUAL, then=Value(0)), default=Value(1), output_field=IntegerField()))
diff --git a/tests/test_announcements.py b/tests/test_announcements.py
index 0ec4c0b..593ff34 100644
--- a/tests/test_announcements.py
+++ b/tests/test_announcements.py
@@ -84,6 +84,28 @@ def test_due_unread_message_calls_once_with_optional_api_key(announcement_data,
     assert post.call_args.kwargs["headers"] == ({"Idempotency-Key": job.idempotency_key, "X-API-Key": api_key} if api_key else {"Idempotency-Key": job.idempotency_key})
 
 
+def test_worker_locks_only_announcement_rows_with_nullable_relations(announcement_data, monkeypatch):
+    category, staff, customer, _ = announcement_data
+    ticket = create_ticket(customer=customer, created_by=staff, category=category, subject="پیگیری تماس", body="پیام نخست")
+    job = AnnouncementJob.objects.get(message__ticket=ticket)
+    due(job)
+    manager = AnnouncementJob.objects
+    original = manager.select_for_update
+    lock_targets = []
+
+    def capture_lock(*args, **kwargs):
+        queryset = original(*args, **kwargs)
+        lock_targets.append(queryset.query.select_for_update_of)
+        return queryset
+
+    monkeypatch.setattr(manager, "select_for_update", capture_lock)
+    with patch("apps.integrations.announcements.requests.post", return_value=Mock(content=b"")):
+        call_command("process_notifications", once=True)
+    job.refresh_from_db()
+    assert job.status == AnnouncementJob.Status.SENT
+    assert lock_targets == [("self",), ("self",)]
+
+
 def test_customer_read_cancels_only_that_message(announcement_data):
     category, staff, customer, _ = announcement_data
     ticket = create_ticket(customer=customer, created_by=staff, category=category, subject="پیگیری مشتری", body="پیام نخست")