diff --git a/frontend/src/hooks/useNotifications.ts b/frontend/src/hooks/useNotifications.ts
index 28c85c4..99f003a 100644
--- a/frontend/src/hooks/useNotifications.ts
+++ b/frontend/src/hooks/useNotifications.ts
@@ -49,6 +49,9 @@ export function NotificationProvider({ children }: { children: ReactNode }) {
       return data.count;
     },
     refetchInterval: 15_000,
+    // Required: toast notifications depend on background polling to detect new
+    // notifications when the tab is hidden (e.g. user switches to sender tab).
+    refetchIntervalInBackground: true,
     staleTime: 10_000,
   });