UnicodeDecodeError during fits.Header.fromfile()

MWE:

import numpy as np
from astropy.io import fits

fn = 'test.fits'
data = np.random.randn(1, 1)
hdu = fits.HDUList(fits.PrimaryHDU(data))
hdu.writeto(fn, overwrite=True)
header = fits.Header.fromfile(fn)

produces:

---------------------------------------------------------------------------
UnicodeDecodeError                        Traceback (most recent call last)
<ipython-input-2-32a656c8e40e> in <module>
      6 hdu = fits.HDUList(fits.PrimaryHDU(data))
      7 hdu.writeto(fn, overwrite=True)
----> 8 header = fits.Header.fromfile(fn)

/usr/local/lib/python3.6/dist-packages/astropy/io/fits/header.py in fromfile(cls, fileobj, sep, endcard, padding)
    445 
    446             return cls._from_blocks(block_iter, is_binary, sep, endcard,
--> 447                                     padding)[1]
    448         finally:
    449             if close_file:

/usr/local/lib/python3.6/dist-packages/astropy/io/fits/header.py in _from_blocks(cls, block_iter, is_binary, sep, endcard, padding)
    474         # Read the first header block.
    475         try:
--> 476             block = next(blocks)
    477         except StopIteration:
    478             raise EOFError()

/usr/local/lib/python3.6/dist-packages/astropy/io/fits/header.py in block_iter(nbytes)
    437             def block_iter(nbytes):
    438                 while True:
--> 439                     data = fileobj.read(nbytes)
    440 
    441                     if data:

/usr/lib/python3.6/codecs.py in decode(self, input, final)
    319         # decode input (taking the buffer into account)
    320         data = self.buffer + input
--> 321         (result, consumed) = self._buffer_decode(data, self.errors, final)
    322         # keep undecoded input until the next call
    323         self.buffer = data[consumed:]

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xa4 in position 2883: invalid start byte

However, opening the file in binary mode seems to work:

with open(fn, 'rb') as fp:
    header = fits.Header.fromfile(fp)

[astromancer]

I closed this before realising @embray had done some additional work on the PR. Keeping open for now.

[bsipocz]

@astromancer - Please open a PR if you think you have the fix.