diff --git a/src/epub_converter/epub_converter.py b/src/epub_converter/epub_converter.py
index 668e340..4f0ab58 100644
--- a/src/epub_converter/epub_converter.py
+++ b/src/epub_converter/epub_converter.py
@@ -279,8 +279,9 @@ class EpubConverter:
         for html_href, soup in self.html_href2html_body_soup.items():
             for i in self.html_href2subchapters_ids[html_href]:
                 tag = soup.find(id=i)
-                # in order not to lose tags in verification of same level of chapter
-                parent_tag = tag.find_parents(['p', 'span', 'h1', 'h2', 'h3', 'h4', 'h5'])[-1]
+                # in order not to lose tags in verification of same level in chapter
+                parent_tags = tag.find_parents(['p', 'span', 'h1', 'h2', 'h3', 'h4', 'h5'])
+                parent_tag = parent_tags[-1] if parent_tags else tag
                 tmp_tag = soup.new_tag("lc_tmp")
                 tmp_tag.attrs["class"] = "converter-chapter-mark"
                 tmp_tag.attrs["id"] = i