400 Bad request

[jacopsd]

Using python 3.6, trying a dry run I get:

rotate-backups-s3 --dry-run --hourly=24 my-bucket
2018-04-20 05:24:10 rotate_backups_s3.cli[8952] INFO Performing a dry run (because of --dry-run option) ..
Traceback (most recent call last):
  File "/home/me/.virtualenvs/EXP3.6/bin/rotate-backups-s3", line 11, in <module>
    load_entry_point('rotate-backups-s3==0.4', 'console_scripts', 'rotate-backups-s3')()
  File "/home/me/.virtualenvs/EXP3.6/lib/python3.6/site-packages/rotate_backups_s3/cli.py", line 205, in main
    ).rotate_backups(bucket, prefix)
  File "/home/me/.virtualenvs/EXP3.6/lib/python3.6/site-packages/rotate_backups_s3/__init__.py", line 131, in rotate_backups
    bucket = self.conn.get_bucket(bucketname)
  File "/home/me/.virtualenvs/EXP3.6/lib/python3.6/site-packages/boto/s3/connection.py", line 509, in get_bucket
    return self.head_bucket(bucket_name, headers=headers)
  File "/home/me/.virtualenvs/EXP3.6/lib/python3.6/site-packages/boto/s3/connection.py", line 556, in head_bucket
    response.status, response.reason, body)
boto.exception.S3ResponseError: S3ResponseError: 400 Bad Request

Any clue? Boto3 commands do work