diff --git a/site/src/lib/dataloader.ts b/site/src/lib/dataloader.ts
index 032c8b8..b37b8fb 100644
--- a/site/src/lib/dataloader.ts
+++ b/site/src/lib/dataloader.ts
@@ -62,12 +62,14 @@ function isYearShardUrl(url: string): boolean {
 }
 
 function rewriteActivityUrls(a: ActivitySummary, shardBase: string): ActivitySummary {
+  // Skip if URL is already absolute (http:// or root-relative /) — avoids
+  // double-rewriting when shards are nested (e.g. user shard → year shard).
+  const needsRewrite = (url: string | null | undefined): boolean =>
+    !!url && !url.startsWith('http') && !url.startsWith('/');
   return {
     ...a,
-    detail_url: a.detail_url && !a.detail_url.startsWith('http')
-      ? `${shardBase}${a.detail_url}` : a.detail_url,
-    track_url: a.track_url && !a.track_url.startsWith('http')
-      ? `${shardBase}${a.track_url}` : a.track_url,
+    detail_url: needsRewrite(a.detail_url) ? `${shardBase}${a.detail_url}` : a.detail_url,
+    track_url:  needsRewrite(a.track_url)  ? `${shardBase}${a.track_url}`  : a.track_url,
   };
 }