diff --git a/pyext/rivet/hepdatautils.py b/pyext/rivet/hepdatautils.py
--- a/pyext/rivet/hepdatautils.py
+++ b/pyext/rivet/hepdatautils.py
@@ -1,77 +1,76 @@
 from __future__ import print_function
 
 def compare_with_hepdata(yodafile, inspire_id=0, yodafile_from_hepdata=None, output=None):
     """\
     Compare a YODA reference data file, intended for inclusion in Rivet, with the YODA file downloaded from HEPData.
     Make the comparison using the yodadiff script distributed with YODA (https://yoda.hepforge.org/trac/browser/bin/yodadiff).
 
     :param yodafile: name of YODA reference data file (intended for inclusion in Rivet)
     :param inspire_id: INSPIRE ID (to download the YODA file from HEPData)
     :param yodafile_from_hepdata: name of YODA file already downloaded from HEPData
     :param output: name of output file for yodadiff instead of stdout (note: -o option of yodadiff not implemented)
     :return: True or False depending on whether YODA files are compatible
     """
 
     if inspire_id:
         # Extract Rivet analysis name from last pathname component of yodafile (and discard extension).
         import os
         tail = os.path.split(yodafile)[1]
         rivet_analysis_name = os.path.splitext(tail)[0]
         yodafile_from_hepdata = download_from_hepdata(inspire_id, rivet_analysis_name)
 
     if yodafile_from_hepdata:
         print('Comparing {} with {}'.format(yodafile, yodafile_from_hepdata))
         import subprocess
         args = ['yodadiff', yodafile, yodafile_from_hepdata]
         if output:
             print('Writing output of "{}" to {}'.format(' '.join(args), output))
             with open(output, 'w') as out:
                 # Note: -o|--output option of yodadiff is not implemented.
                 exit_status = subprocess.call(args, stdout=out, stderr=out)
         else:
             exit_status = subprocess.call(args)
         if exit_status:
             return False
     else:
         print('No YODA file from HEPData specified!')
         return False
 
     return True
 
 
 def download_from_hepdata(inspire_id, rivet_analysis_name=None):
     """\
     Download the latest YODA reference data file from HEPData identified by the INSPIRE ID.
     Optionally pass the Rivet analysis name to write in the YODA file exported from HEPData.
 
     :param inspire_id: INSPIRE ID
     :param rivet_analysis_name: Rivet analysis name to override default
     :return: name of YODA file downloaded from HEPData
     """
 
     import tarfile, io, os, requests
 
     hdurl = 'https://hepdata.net/record/ins{}'.format(inspire_id)
     payload = {'format': 'yoda', 'rivet': rivet_analysis_name}
     response = requests.get(hdurl, params=payload)
     if response.history:
         print('Downloading from {}'.format(response.history[0].url))
     else:
         print('Downloading from {}'.format(response.url))
 
     if response.status_code != 200:
         print('Download failed ({} {}), does {} exist?'.format(response.status_code, response.reason, hdurl))
         return None
 
     try:
         tar = tarfile.open(mode='r:gz', fileobj=io.BytesIO(response.content))
         tar.extractall()
         yodafile_from_hepdata = tar.getnames()[0]
-        os.chmod(yodafile_from_hepdata, 0644)
+        os.chmod(yodafile_from_hepdata, 0o644)
     except tarfile.TarError as e:
         print('Error reading tarfile ({})'.format(str(e)))
         return None
 
     print('Downloaded {}'.format(yodafile_from_hepdata))
     return yodafile_from_hepdata
-