UnicodeDecodeError: 'utf8' codec can't decode byte 0xad in position 9107: invalid start byte

[reckoner]

Traceback (most recent call last):
  File "/usr/bin/em", line 11, in <module>
    sys.exit(main())
  File "/usr/lib/python2.7/site-packages/em/__init__.py", line 221, in main
    emphasize(stream, patterns)
  File "/usr/lib/python2.7/site-packages/em/__init__.py", line 126, in emphasize
    for line in iterate_over_stream(stream):
  File "/usr/lib/python2.7/site-packages/em/__init__.py", line 83, in iterate_over_stream
    for line in buf.decode(sys.getfilesystemencoding()).splitlines():
  File "/usr/lib/python2.7/encodings/utf_8.py", line 16, in decode
    return codecs.utf_8_decode(input, errors, True)
UnicodeDecodeError: 'utf8' codec can't decode byte 0xad in position 9107: invalid start byte