diff --git a/src/epub_converter/epub_converter.py b/src/epub_converter/epub_converter.py
index a0a9f24..35ba909 100644
--- a/src/epub_converter/epub_converter.py
+++ b/src/epub_converter/epub_converter.py
@@ -440,7 +440,7 @@ class EpubConverter:
                                                                   path_to_html=nav_point.href,
                                                                   access=self.access,
                                                                   path2aws_path=self.old_image_path2aws_path,
-                                                                  book_id=self.file.stem)
+                                                                  book_id=self.file.stem or 'book_id')
 
         is_chapter = lvl <= LiveCartaConfig.SUPPORTED_LEVELS
         title_preprocessed = prepare_title(title)