diff --git a/services/web/frontend/js/features/source-editor/languages/markdown/document-outline.ts b/services/web/frontend/js/features/source-editor/languages/markdown/document-outline.ts
index 7f7a5ea4d8..8c32f667b7 100644
--- a/services/web/frontend/js/features/source-editor/languages/markdown/document-outline.ts
+++ b/services/web/frontend/js/features/source-editor/languages/markdown/document-outline.ts
@@ -33,21 +33,23 @@ const enterMarkdownNode = (
     return
   }
 
-  // Collect heading text, skipping the HeaderMark (the leading # characters)
-  let title = ''
-  const cursor = node.node.cursor()
-  if (cursor.firstChild()) {
-    do {
-      if (cursor.name !== 'HeaderMark') {
-        title += state.sliceDoc(cursor.from, cursor.to)
-      }
-    } while (cursor.nextSibling())
-  }
+  // In the Lezer Markdown grammar the heading text is NOT a child node —
+  // the only children are HeaderMark nodes ('#'s for ATX, the '='/'-'
+  // underline for Setext). The title text sits in the gaps between marks.
+  // So we slice the whole heading and strip the marker characters:
+  //  - ATX:    leading '#'s and any optional trailing '#'s
+  //  - Setext: the trailing underline line ('===' / '---')
+  const raw = state.sliceDoc(node.from, node.to)
+  const title = raw
+    .replace(/^\s*#+\s*/, '') // ATX: leading ### markers
+    .replace(/\s*#+\s*$/, '') // ATX: optional closing ### markers
+    .replace(/\n[=-]+\s*$/, '') // Setext: underline line
+    .trim()
 
   items.push({
     line: state.doc.lineAt(node.from).number,
     toLine: state.doc.lineAt(node.to).number,
-    title: title.trim(),
+    title,
     from: node.from,
     to: node.to,
     level,