diff --git a/package-lock.json b/package-lock.json
index a53aa18..778558f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "instaarchive-viewer",
-  "version": "1.5.0",
+  "version": "1.5.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "instaarchive-viewer",
-      "version": "1.5.0",
+      "version": "1.5.1",
       "dependencies": {
         "@tailwindcss/vite": "^4.1.14",
         "@vitejs/plugin-react": "^5.0.4",
diff --git a/package.json b/package.json
index 6d81a34..2b704b4 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "instaarchive-viewer",
   "private": true,
-  "version": "1.5.0",
+  "version": "1.5.1",
   "type": "module",
   "scripts": {
     "dev": "vite --port=3000 --host=0.0.0.0",
diff --git a/src/lib/archive-index.test.ts b/src/lib/archive-index.test.ts
new file mode 100644
index 0000000..393e094
--- /dev/null
+++ b/src/lib/archive-index.test.ts
@@ -0,0 +1,34 @@
+import { describe, expect, it } from 'vitest';
+import { isSystemDirectory } from './archive-index';
+
+describe('isSystemDirectory', () => {
+  it.each([
+    ['@eaDir', 'Synology thumbnail/index metadata, written inside every folder'],
+    ['@tmp', 'Synology scratch'],
+    ['.sync', 'Resilio state'],
+    ['.DS_Store', 'macOS'],
+    ['#recycle', 'Synology deletions'],
+    ['#snapshot', 'Synology snapshots'],
+  ])('skips %s (%s)', name => {
+    expect(isSystemDirectory(name)).toBe(true);
+  });
+
+  it.each([
+    '4utumn07',
+    '4utumn07 - reels',
+    'story - dawn_petal',
+    'story highlights - official_band - A.B.C',
+    'story highlights - theoldlyricmuseinsta - 💙1999-2005 era',
+    'Heejin_Bubble heejinmedia',
+    'gallery-dl',
+    'posts',
+  ])('keeps %s', name => {
+    expect(isSystemDirectory(name)).toBe(false);
+  });
+
+  it('does not treat a leading underscore as a system directory', () => {
+    // `_gemini-plans` is filtered separately at the archive root only; nothing
+    // below the root should be excluded just for starting with an underscore.
+    expect(isSystemDirectory('_gemini-plans')).toBe(false);
+  });
+});
diff --git a/src/lib/archive-index.ts b/src/lib/archive-index.ts
index a7bf6e8..8fb0826 100644
--- a/src/lib/archive-index.ts
+++ b/src/lib/archive-index.ts
@@ -33,6 +33,21 @@ interface DirIndex {
 const MEDIA_RE = /\.(jpg|jpeg|png|webp|gif|bmp|tiff|mp4|webm|ogv|mov)$/i;
 const STAT_CONCURRENCY = 16;
 
+/**
+ * Directories the walk must never descend into.
+ *
+ * NAS filesystems scatter sidecar metadata *inside* every folder, not just at
+ * the share root: Synology writes `@eaDir` (thumbnails and indexing data),
+ * `#recycle` holds deletions, and `.sync` is Resilio's state. Indexing those
+ * would count NAS thumbnails as archive media and spend a stat on each one —
+ * measured on a real share, `@eaDir` accounted for 12,516 of 123,023 files.
+ *
+ * The archive root is already filtered by prefix; this is the same rule applied
+ * at every level below it.
+ */
+export const isSystemDirectory = (name: string): boolean =>
+  name.startsWith('@') || name.startsWith('.') || name === '#recycle' || name === '#snapshot';
+
 export class ArchiveIndex {
   private dirs = new Map<string, DirIndex>();
   private inFlight = new Map<string, Promise<DirIndex>>();
@@ -43,7 +58,7 @@ export class ArchiveIndex {
   /** Visible (non-system) directories at the archive root. */
   private listRootDirs(): string[] {
     return fs.readdirSync(this.archivesDir, { withFileTypes: true })
-      .filter(e => e.isDirectory() && !/^[.@_]/.test(e.name))
+      .filter(e => e.isDirectory() && !isSystemDirectory(e.name) && !e.name.startsWith('_'))
       .map(e => e.name);
   }
 
@@ -69,6 +84,7 @@ export class ArchiveIndex {
       return out;
     }
     for (const entry of entries) {
+      if (isSystemDirectory(entry.name)) continue;
       const rel = base ? `${base}/${entry.name}` : entry.name;
       if (entry.isDirectory()) out = out.concat(this.walk(path.join(absDir, entry.name), rel));
       else if (entry.isFile()) out.push(rel);