diff --git a/src/calibre/ebooks/oeb/polish/create.py b/src/calibre/ebooks/oeb/polish/create.py
index 46a0c0c5fe..1028818a56 100644
--- a/src/calibre/ebooks/oeb/polish/create.py
+++ b/src/calibre/ebooks/oeb/polish/create.py
@@ -22,6 +22,7 @@ from calibre.ebooks.oeb.polish.toc import TOC, create_ncx
 from calibre.utils.localization import lang_as_iso639_1
 from calibre.utils.logging import DevNull
 from calibre.utils.zipfile import ZipFile, ZIP_STORED
+from polyglot.builtins import as_bytes
 
 valid_empty_formats = {'epub', 'txt', 'docx', 'azw3'}
 
@@ -42,7 +43,7 @@ def create_book(mi, path, fmt='epub', opf_name='metadata.opf', html_name='start.
     if fmt == 'txt':
         with open(path, 'wb') as f:
             if not mi.is_null('title'):
-                f.write(mi.title)
+                f.write(as_bytes(mi.title))
         return
     if fmt == 'docx':
         from calibre.ebooks.conversion.plumber import Plumber