diff --git a/src/calibre/ebooks/mobi/debug/headers.py b/src/calibre/ebooks/mobi/debug/headers.py
index 308d7c262b..ef4fe8f6eb 100644
--- a/src/calibre/ebooks/mobi/debug/headers.py
+++ b/src/calibre/ebooks/mobi/debug/headers.py
@@ -6,14 +6,14 @@ __license__   = 'GPL v3'
 __copyright__ = '2012, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-import struct, datetime, os, numbers
+import struct, datetime, os, numbers, binascii
 
 from calibre.utils.date import utc_tz
 from calibre.ebooks.mobi.reader.headers import NULL_INDEX
 from calibre.ebooks.mobi.langcodes import main_language, sub_language
 from calibre.ebooks.mobi.debug import format_bytes
 from calibre.ebooks.mobi.utils import get_trailing_data
-from polyglot.builtins import as_bytes, iteritems, range, unicode_type
+from polyglot.builtins import iteritems, range, unicode_type
 
 # PalmDB {{{
 
@@ -210,7 +210,7 @@ class EXTHRecord(object):
             else:
                 self.data, = struct.unpack(b'>L', self.data)
         elif self.type in {209, 300}:
-            self.data = as_bytes(self.data.encode('hex'))
+            self.data = binascii.hexlify(self.data)
 
     def __str__(self):
         return '%s (%d): %r'%(self.name, self.type, self.data)