diff --git a/articles/mobile-apps/includes/notification-hubs-backend-service-web-api.md b/articles/mobile-apps/includes/notification-hubs-backend-service-web-api.md
index 23d9a0a23f..387cb7630e 100644
--- a/articles/mobile-apps/includes/notification-hubs-backend-service-web-api.md
+++ b/articles/mobile-apps/includes/notification-hubs-backend-service-web-api.md
@@ -321,6 +321,7 @@ Use of the notification hub and the [Notification Hubs SDK for backend operation
 1. Add an **Empty Interface** to the **Services** folder called *INotificationService.cs*, then add the following implementation.
 
     ```csharp
+    using System.Threading;
     using System.Threading.Tasks;
     using PushDemoApi.Models;