diff --git a/web/ui/app.js b/web/ui/app.js
index 7f7e980..fe7c542 100644
--- a/web/ui/app.js
+++ b/web/ui/app.js
@@ -202,9 +202,13 @@ async function browseWavs() {
 
   try {
     const resp = await fetch(`${API}/list-wavs?dir=${encodeURIComponent(dir)}`);
+    if (!resp.ok) {
+      list.innerHTML = '<span class="no-files">HTTP ' + resp.status + '</span>';
+      return;
+    }
     const data = await resp.json();
-    if (data.error) {
-      list.innerHTML = '<span class="no-files">Error: ' + data.error + '</span>';
+    if (!data || data.error) {
+      list.innerHTML = '<span class="no-files">Error: ' + (data && data.error ? data.error : 'server error') + '</span>';
       return;
     }
     if (!Array.isArray(data) || data.length === 0) {