diff --git a/swh/loader/tar/loader.py b/swh/loader/tar/loader.py
index 2192c2c..ab17f0b 100644
--- a/swh/loader/tar/loader.py
+++ b/swh/loader/tar/loader.py
@@ -1,114 +1,113 @@
 # Copyright (C) 2015  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import logging
 import os
 import tempfile
 import shutil
 import sys
 import traceback
 
 from swh.loader.dir import loader
 from swh.loader.tar import tarball
 
 
 class TarLoader(loader.DirLoader):
     """A tarball loader.
 
     """
     def __init__(self, config):
         super().__init__(config)
         self.log = logging.getLogger('swh.loader.tar.TarLoader')
 
     def process(self, tarpath, origin, revision, release, occurrences):
         """Load a tarball in backend.
 
         This will:
         - persist the origin if it does not exist.
         - write an entry in fetch_history to mark the loading tarball start
         - uncompress locally the tarballs in a temporary location
         - process the content of the tarballs to persist on swh storage
         - clean up the temporary location
         - write an entry in fetch_history to mark the loading tarball end
 
         Args:
             - tarpath: path to the tarball to uncompress
             - origin: Dictionary origin
               - url: url origin we fetched
               - type: type of the origin
             - revision: Dictionary of information needed, keys are:
               - author_name: revision's author name
               - author_email: revision's author email
               - author_date: timestamp (e.g. 1444054085)
               - author_offset: date offset e.g. -0220, +0100
               - committer_name: revision's committer name
               - committer_email: revision's committer email
               - committer_date: timestamp
               - committer_offset: date offset e.g. -0220, +0100
               - type: type of revision dir, tar
               - message: synthetic message for the revision
             - release: Dictionary of information needed, keys are:
               - name: release name
               - date: release timestamp (e.g. 1444054085)
               - offset: release date offset e.g. -0220, +0100
               - author_name: release author's name
               - author_email: release author's email
               - comment: release's comment message
             - occurrences: List of occurrence dictionary.
               Information needed, keys are:
               - branch: occurrence's branch name
               - authority_id: authority id (e.g. 1 for swh)
               - validity: validity date (e.g. 2015-01-01 00:00:00+00)
 
         """
         if 'type' not in origin:  # let the type flow if present
             origin['type'] = 'tar'
         origin['id'] = self.storage.origin_add_one(origin)
 
         # Mark the start of the loading
         fetch_history_id = self.open_fetch_history(origin['id'])
 
         # Prepare the extraction path
         extraction_dir = self.config['extraction_dir']
         os.makedirs(extraction_dir, 0o755, exist_ok=True)
         dir_path = tempfile.mkdtemp(prefix='swh.loader.tar-',
                                     dir=extraction_dir)
 
         # T62:
         # - create tarball as content in storage
         # - transit the information to the loader dir
 
         # T22: add checksums in revision
 
         # for edge cases (NotImplemented...)
         result = {'status': False, 'stderr': ''}
 
         try:
             self.log.info('Uncompress %s to %s' % (tarpath, dir_path))
             tarball.uncompress(tarpath, dir_path)
 
             result = super().process(dir_path, origin, revision, release,
                                      occurrences)
-
         except:
             e_info = sys.exc_info()
             if not result['status']:
                 # Enrich the error message with the tarball
-                result['stderr'] = 'reason: %s\ntrace: %s\n%s' % (
+                result['stderr'] = 'reason:%s\ntrace:%s\n%s' % (
                     e_info[1],
                     ''.join(traceback.format_tb(e_info[2])),
                     result.get('stderr', ''))
 
             raise
         finally:
             shutil.rmtree(dir_path)
 
             if not result['status']:
-                result['stderr'] = 'archive:%s\n%s' % (
+                result['stderr'] = 'archive:%s\nreason:%s' % (
                     tarpath,
                     result.get('stderr', ''))
 
             # mark the end of the loading
             self.close_fetch_history(fetch_history_id, result)