diff --git a/static/js/utils.js b/static/js/utils.js
index cba53a9..b3b59c6 100644
--- a/static/js/utils.js
+++ b/static/js/utils.js
@@ -358,9 +358,9 @@ function ttvcIsLowMemoryDevice() {
 window.ttvcIsLowMemoryDevice = ttvcIsLowMemoryDevice;
 // Run an async worker over items with bounded concurrency (default 4). `onProgress(done,total)`
 // fires after each item. Replaces slow serial `for…await` loops over network calls.
-async function runPool(items, worker, concurrency = 4, onProgress) {
+async function runPool(items, worker, concurrency, onProgress) {
   const arr = [...items]; let i = 0, done = 0; const total = arr.length;
-  const requested = Math.max(1, Number(concurrency) || 1);
+  const requested = Math.max(1, Number(concurrency ?? 4) || 1);
   const effectiveConcurrency = ttvcIsLowMemoryDevice() ? Math.min(2, requested) : requested;
   async function run() {
     while (i < arr.length) {