diff --git a/frontend/src/banner.ts b/frontend/src/banner.ts
index e34e240..1c6d63b 100644
--- a/frontend/src/banner.ts
+++ b/frontend/src/banner.ts
@@ -17,6 +17,11 @@ function notify() {
 }
 
 function show(severity: BannerSeverity, message: string): void {
+  const isDuplicate = banners.some(
+    (b) => b.severity === severity && b.message === message,
+  );
+  if (isDuplicate) return;
+
   const id = nextId++;
   banners = [{ id, severity, message }, ...banners];
   notify();