diff --git a/static/js/app.js b/static/js/app.js
index 97c1309..1a1b1e1 100644
--- a/static/js/app.js
+++ b/static/js/app.js
@@ -2725,6 +2725,22 @@ function _injectImageBlobs(html, chapterDir, imageMap) {
   return html;
 }
 
+// EPUBs mark footnote/endnote reference links very inconsistently across
+// editions/tools — some use class="footnote" (same-file '#frag' href), some
+// use the EPUB3 epub:type="noteref" attribute, and some (e.g. older
+// Calibre/zeno.org conversions) use neither and just wrap a plain link to
+// another chapter file's fragment in a <sup> — in either direction
+// (<sup><a>…</a></sup> or <a><sup>…</sup></a>). Recognize all of these
+// rather than only the single hardcoded class name.
+function _looksLikeFootnoteLink(el, href) {
+  if (!href.includes('#')) return false;
+  const cls = (el.getAttribute('class') || '').toLowerCase();
+  if (/\bnote|\bfootnote|\bfn\b/.test(cls)) return true;
+  const epubType = (el.getAttribute('epub:type') || '').toLowerCase();
+  if (epubType.includes('noteref')) return true;
+  return !!(el.closest('sup') || el.querySelector('sup'));
+}
+
 function sanitizeEpubHtml(html) {
   const doc = new DOMParser().parseFromString(html, 'text/html');
 
@@ -2745,8 +2761,12 @@ function sanitizeEpubHtml(html) {
       if (href.startsWith('http://') || href.startsWith('https://')) {
         el.setAttribute('target', '_blank');
         el.setAttribute('rel', 'noopener noreferrer');
-      } else if (el.classList.contains('footnote') && href.startsWith('#')) {
-        el.dataset.footnoteRef = href.slice(1);
+      } else if (_looksLikeFootnoteLink(el, href)) {
+        // The whole book is one concatenated DOM, so a fragment id resolves
+        // via getElementById regardless of which chapter file it originally
+        // pointed into — strip any "../Text/other.html" path prefix and keep
+        // just the id after the last '#'.
+        el.dataset.footnoteRef = href.slice(href.indexOf('#') + 1);
         el.removeAttribute('href');
         el.style.cursor = 'pointer';
       } else {
diff --git a/static/js/sw.js b/static/js/sw.js
index 4bcf391..41ab2c4 100644
--- a/static/js/sw.js
+++ b/static/js/sw.js
@@ -2,7 +2,7 @@
  * diora service worker — caches the app shell for offline use.
  */
 
-const CACHE = 'diora-v30';
+const CACHE = 'diora-v31';
 const PODCAST_CACHE = 'diora-podcast-v1';
 const SHELL = [
   '/static/css/app.css',