diff --git a/packages/client/src/tiptap/core/extensions/title.tsx b/packages/client/src/tiptap/core/extensions/title.tsx
index c0712d5..386764b 100644
--- a/packages/client/src/tiptap/core/extensions/title.tsx
+++ b/packages/client/src/tiptap/core/extensions/title.tsx
@@ -74,7 +74,7 @@ export const Title = Node.create<TitleOptions>({
 
               const $head = state.selection.$head;
               const titleNode = $head.node($head.depth);
-              const endPos = titleNode.firstChild.nodeSize + 1;
+              const endPos = ((titleNode.firstChild && titleNode.firstChild.nodeSize) || 0) + 1;
 
               dispatch(state.tr.insert(endPos, paragraph.create()));
 
diff --git a/packages/client/src/tiptap/markdown/prosemirror-to-markdown/helpers.ts b/packages/client/src/tiptap/markdown/prosemirror-to-markdown/helpers.ts
index c40548d..7b2d7d1 100644
--- a/packages/client/src/tiptap/markdown/prosemirror-to-markdown/helpers.ts
+++ b/packages/client/src/tiptap/markdown/prosemirror-to-markdown/helpers.ts
@@ -132,7 +132,9 @@ export function openTag(tagName, attrs) {
   str += Object.entries(attrs || {})
     .map(([key, value]) => {
       if ((ignoreAttrs[tagName] || []).includes(key) || defaultAttrs[tagName]?.[key] === value) return '';
-
+      if (!['class', 'id'].includes(key) && !key.startsWith('data-')) {
+        key = `data-${key}`;
+      }
       return ` ${key}="${htmlEncode(value?.toString())}"`;
     })
     .join('');
diff --git a/packages/client/src/tiptap/markdown/prosemirror-to-markdown/index.ts b/packages/client/src/tiptap/markdown/prosemirror-to-markdown/index.ts
index 3232c27..06b719a 100644
--- a/packages/client/src/tiptap/markdown/prosemirror-to-markdown/index.ts
+++ b/packages/client/src/tiptap/markdown/prosemirror-to-markdown/index.ts
@@ -158,7 +158,7 @@ const SerializerConfig = {
       state.renderList(node, '  ', () => (node.attrs.bullet || '*') + ' ');
     },
     [Text.name]: defaultMarkdownSerializer.nodes.text,
-    [Title.name]: renderCustomContainer('title'),
+    [Title.name]: renderHTMLNode('div', false, true, { class: 'title' }),
   },
 };