diff --git a/src/app/api/browse/route.ts b/src/app/api/browse/route.ts
index 63cf227..0433488 100644
--- a/src/app/api/browse/route.ts
+++ b/src/app/api/browse/route.ts
@@ -30,7 +30,7 @@ export async function GET(request: NextRequest) {
   const root = resolveLibraryRoot(library)
   const recursive = request.nextUrl.searchParams.get('recursive') === 'true'
   const listing = recursive
-    ? scanDirectoryRecursive(root, libraryId, subpath)
+    ? await scanDirectoryRecursive(root, libraryId, subpath)
     : scanDirectory(root, libraryId, subpath)
 
   // Annotate image files with hasExtractedText, and directories if any descendant has extracted text
diff --git a/src/lib/files.ts b/src/lib/files.ts
index 73fa333..2a06ed7 100644
--- a/src/lib/files.ts
+++ b/src/lib/files.ts
@@ -74,12 +74,16 @@ export function scanDirectory(
  * Recursively walks every subdirectory under `subpath` and returns a flat list
  * of all files. Directory entries are omitted. Each FileEntry.name is the full
  * relative path from the library root (e.g. FolderA/SubFolder/video.mp4).
+ *
+ * Uses async I/O so the Node.js event loop is not blocked during large
+ * directory trees (blocking stalls streaming responses and causes
+ * "ReadableStream is already closed" errors on concurrent requests).
  */
-export function scanDirectoryRecursive(
+export async function scanDirectoryRecursive(
   libraryRoot: string,
   libraryId: string,
   subpath: string
-): DirectoryListing {
+): Promise<DirectoryListing> {
   let rootAbsPath: string
   try {
     rootAbsPath = subpath ? resolveAndJail(libraryRoot, subpath) : libraryRoot
@@ -89,35 +93,37 @@ export function scanDirectoryRecursive(
 
   const entries: FileEntry[] = []
 
-  function walk(absDir: string, relDir: string): void {
+  async function walk(absDir: string, relDir: string): Promise<void> {
     let dirents: fs.Dirent[]
     try {
-      dirents = fs.readdirSync(absDir, { withFileTypes: true })
+      dirents = await fs.promises.readdir(absDir, { withFileTypes: true })
     } catch {
       return
     }
-    for (const d of dirents) {
-      if (HIDDEN_FILES.test(d.name)) continue
-      const relPath = relDir ? path.join(relDir, d.name) : d.name
-      if (d.isDirectory()) {
-        walk(path.join(absDir, d.name), relPath)
-      } else {
-        const mediaType = getMediaType(d.name)
-        const hasThumbnail = mediaType === 'image' || mediaType === 'video'
-        // name = full relative path from library root so media keys match
-        const fullRelPath = subpath ? path.join(subpath, relPath) : relPath
-        entries.push({
-          name: fullRelPath,
-          type: 'file',
-          mediaType,
-          url: fileApiUrl(libraryId, fullRelPath),
-          thumbnailUrl: hasThumbnail ? thumbnailApiUrl(libraryId, fullRelPath) : null,
-        })
-      }
-    }
+    await Promise.all(
+      dirents.map(async (d) => {
+        if (HIDDEN_FILES.test(d.name)) return
+        const relPath = relDir ? path.join(relDir, d.name) : d.name
+        if (d.isDirectory()) {
+          await walk(path.join(absDir, d.name), relPath)
+        } else {
+          const mediaType = getMediaType(d.name)
+          const hasThumbnail = mediaType === 'image' || mediaType === 'video'
+          // name = full relative path from library root so media keys match
+          const fullRelPath = subpath ? path.join(subpath, relPath) : relPath
+          entries.push({
+            name: fullRelPath,
+            type: 'file',
+            mediaType,
+            url: fileApiUrl(libraryId, fullRelPath),
+            thumbnailUrl: hasThumbnail ? thumbnailApiUrl(libraryId, fullRelPath) : null,
+          })
+        }
+      })
+    )
   }
 
-  walk(rootAbsPath, '')
+  await walk(rootAbsPath, '')
   entries.sort((a, b) => a.name.localeCompare(b.name))
   return { path: subpath, entries }
 }