diff --git a/src/calibre/ebooks/pdb/haodoo/reader.py b/src/calibre/ebooks/pdb/haodoo/reader.py
index a27d0cba0d..1474625a0d 100644
--- a/src/calibre/ebooks/pdb/haodoo/reader.py
+++ b/src/calibre/ebooks/pdb/haodoo/reader.py
@@ -19,8 +19,8 @@ from calibre.ebooks.metadata import MetaInformation
 from calibre.ebooks.txt.processor import opf_writer, HTML_TEMPLATE
 from polyglot.builtins import range, map
 
-BPDB_IDENT = b'BOOKMTIT'
-UPDB_IDENT = b'BOOKMTIU'
+BPDB_IDENT = 'BOOKMTIT'
+UPDB_IDENT = 'BOOKMTIU'
 
 punct_table = {
     u"︵": u"（",