Another error with py3-cairo

[Walter Schwarzenfeld]

I got following error for all ".c" files in src:

Traceback (most recent call last):
   File 
"/ram/usr/ports/graphics/py3-cairo/work/pycairo-1.10.0/.waf3-1.6.4-e3c1e08604b18a10567cfcd2d02eb6e6/waflib/Tools/c_preproc.py", 
line 496, in addlines
     lines=filter_comments(filepath)
   File 
"/ram/usr/ports/graphics/py3-cairo/work/pycairo-1.10.0/.waf3-1.6.4-e3c1e08604b18a10567cfcd2d02eb6e6/waflib/Tools/c_preproc.py", 
line 47, in filter_comments
     code=Utils.readf(filename)
   File 
"/ram/usr/ports/graphics/py3-cairo/work/pycairo-1.10.0/.waf3-1.6.4-e3c1e08604b18a10567cfcd2d02eb6e6/waflib/Utils.py", 
line 83, in readf
     txt=f.read()
   File "/usr/local/lib/python3.6/encodings/ascii.py", line 26, in decode
     return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc2 in position 54: 
ordinal not in range(128)