diff --git a/static/js/app.js b/static/js/app.js
index 29444e5..a784093 100644
--- a/static/js/app.js
+++ b/static/js/app.js
@@ -508,6 +508,9 @@
 
       const newContent = doc.getElementById('content');
       const oldContent = document.getElementById('content');
+      // Read the marker off newContent — replaceWith() reparents that node into
+      // the live document, so `doc` no longer contains it afterwards.
+      const openSlug = newContent?.querySelector('[data-open-slug]')?.dataset.openSlug || null;
       if (newContent && oldContent) oldContent.replaceWith(newContent);
 
       const newData = doc.getElementById('roux-data');
@@ -515,8 +518,6 @@
         try { POSTS = JSON.parse(newData.textContent) || []; lbBuilt = false; } catch {}
       }
 
-      const openSlug = doc.querySelector('[data-open-slug]')?.dataset.openSlug || null;
-
       document.title = doc.title;
       syncHeadMeta(doc);
       if (push) history.pushState({ url: abs, slug: openSlug || undefined }, '', abs);