diff --git a/src/calibre/ebooks/conversion/plugins/mobi_input.py b/src/calibre/ebooks/conversion/plugins/mobi_input.py
index 9d71b69891..49a57cbde1 100644
--- a/src/calibre/ebooks/conversion/plugins/mobi_input.py
+++ b/src/calibre/ebooks/conversion/plugins/mobi_input.py
@@ -59,7 +59,10 @@ class MOBIInput(InputFormatPlugin):
         if mr.kf8_type is not None:
             log('Found KF8 MOBI of type %r'%mr.kf8_type)
             from calibre.ebooks.mobi.reader.mobi8 import Mobi8Reader
-            return os.path.abspath(Mobi8Reader(mr, log)())
+            mr = Mobi8Reader(mr, log)
+            opf = os.path.abspath(mr())
+            self.encrypted_fonts = mr.encrypted_fonts
+            return opf
 
         raw = parse_cache.pop('calibre_raw_mobi_markup', False)
         if raw:
diff --git a/src/calibre/ebooks/mobi/reader/mobi8.py b/src/calibre/ebooks/mobi/reader/mobi8.py
index 7939f51ccf..1e4d63d72e 100644
--- a/src/calibre/ebooks/mobi/reader/mobi8.py
+++ b/src/calibre/ebooks/mobi/reader/mobi8.py
@@ -33,6 +33,7 @@ class Mobi8Reader(object):
     def __init__(self, mobi6_reader, log):
         self.mobi6_reader, self.log = mobi6_reader, log
         self.header = mobi6_reader.book_header
+        self.encrypted_fonts = []
 
     def __call__(self):
         self.mobi6_reader.check_for_drm()
@@ -351,6 +352,8 @@ class Mobi8Reader(object):
                 with open(href.replace('/', os.sep), 'wb') as f:
                     f.write(font['font_data'] if font['font_data'] else
                             font['raw_data'])
+                if font['encrypted']:
+                    self.encrypted_fonts.append(href)
             else:
                 imgtype = imghdr.what(None, data)
                 if imgtype is None:
diff --git a/src/calibre/ebooks/mobi/utils.py b/src/calibre/ebooks/mobi/utils.py
index 2bab82bc53..4c1e52e119 100644
--- a/src/calibre/ebooks/mobi/utils.py
+++ b/src/calibre/ebooks/mobi/utils.py
@@ -437,7 +437,7 @@ def read_font_record(data, extent=1040): # {{{
     # The zlib compressed data begins with 2 bytes of header and
     # has 4 bytes of checksum at the end
     ans = {'raw_data':data, 'font_data':None, 'err':None, 'ext':'failed',
-            'headers':None}
+            'headers':None, 'encrypted':False}
 
     try:
         usize, flags, dstart, xor_len, xor_start = struct.unpack_from(
@@ -460,6 +460,7 @@ def read_font_record(data, extent=1040): # {{{
             buf[n] ^= key[n%xor_len] # XOR of buf and key
 
         font_data = bytes(buf)
+        ans['encrypted'] = True
 
     if flags & 0b1:
         # ZLIB compressed data