diff --git a/frontend/templates/index.html b/frontend/templates/index.html
index a22d8ec..5e41565 100644
--- a/frontend/templates/index.html
+++ b/frontend/templates/index.html
@@ -128,17 +128,31 @@ async function startSession(e) {
   }
   btn.disabled = false;
 }
-
 async function handleUpload(formData) {
   return new Promise((resolve) => {
     const xhr = new XMLHttpRequest();
     xhr.open('POST', '/session/upload');
+    xhr.timeout = 7200000;  // 2 hour timeout for very large uploads
+
     xhr.upload.addEventListener('progress', (e) => {
       if (e.lengthComputable) {
         const pct = Math.round((e.loaded / e.total) * 100);
         setPhase('Uploading source file... ' + (e.loaded / (1024**3)).toFixed(1) + ' GiB', pct, false);
+      } else {
+        // Fallback: show bytes uploaded even without total
+        setPhase('Uploading source file... ' + (e.loaded / (1024**3)).toFixed(1) + ' GiB', 0, true);
       }
     });
+
+    xhr.addEventListener('loadstart', () => {
+      setPhase('Uploading source file...', 0, true);
+    });
+
+    xhr.addEventListener('timeout', () => {
+      setPhase('Upload timed out', 0, false);
+      showError('Upload timed out after 2 hours. The file may be too large for your connection speed. Try downloading the file directly on the server instead.');
+      resolve();
+    });
     xhr.addEventListener('load', async () => {
       if (xhr.status === 200) {
         const data = JSON.parse(xhr.responseText);