diff --git a/ui/src/api/client.ts b/ui/src/api/client.ts
index 4e7fd76..5b928da 100644
--- a/ui/src/api/client.ts
+++ b/ui/src/api/client.ts
@@ -75,6 +75,12 @@ export interface EventQuery {
 
 const API_BASE = '/api/v1';
 
+/** Decode base64 content as UTF-8 (atob only handles Latin-1). */
+function decodeBase64Utf8(b64: string): string {
+  const bytes = Uint8Array.from(atob(b64), (c) => c.charCodeAt(0));
+  return new TextDecoder().decode(bytes);
+}
+
 export async function fetchEvents(q: EventQuery): Promise<TimelineItem[]> {
   const params = new URLSearchParams();
   if (q.from) params.set('from', q.from.toISOString());
@@ -109,7 +115,7 @@ export async function fetchReadme(source: Source, host: string, repo: string): P
     if (!resp.ok) return null;
     const data = await resp.json();
     if (data.encoding === 'base64' && data.content) {
-      return atob(data.content);
+      return decodeBase64Utf8(data.content);
     }
     return data.content ?? null;
   }
@@ -119,7 +125,7 @@ export async function fetchReadme(source: Source, host: string, repo: string): P
       if (!resp.ok) continue;
       const data = await resp.json();
       if (data.encoding === 'base64' && data.content) {
-        return atob(data.content);
+        return decodeBase64Utf8(data.content);
       }
       if (data.content) return data.content;
     }