Error accessing manual in 0.8 test build

The latest manual is working ok on my development system. But when testing in a virtualbox image with plinth-0.8, I get an error:

[2016-02-15 18:39:30,159] django.request ERROR    Internal Server Error: /plinth/help/manual/
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/django/core/handlers/base.py", line 149, in get_response
    response = self.process_exception_by_middleware(e, request)
  File "/usr/lib/python3/dist-packages/django/core/handlers/base.py", line 147, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3/dist-packages/plinth/modules/help/help.py", line 67, in manual
    content = input_file.read()
  File "/usr/lib/python3.5/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 23438: ordinal not in range(128)