Ceph

I am trying to set a policy to a bucket in order to have users that can only read (for debugging purposes). I do it in the following way:

s3cmd --host=ceph-rgw setpolicy policy s3://bucket

The policy is:

{
    "Version": "2012-10-17",
    "Id": "01",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "d.ruiz" 
            },
            "Action": [
                "s3:GetObject",
                "s3:ListBucket" 
            ],
            "Resource": [
                "arn:aws:s3:::bucket/*",
            ]
        }
    ]
}

At the moment I run the setpolicy command, the gateway crashes and logs the following error:

2018-02-12 13:40:43.979192 I | rgw: radosgw: /usr/include/boost/optional/optional.hpp:878: boost::optional<T>::pointer_type boost::optional<T>::operator->() [with T = rgw::IAM::ARN; boost::optional<T>::pointer_type = rgw::IAM::ARN*]: Assertion `this->is_initialized()' failed.
failed to run rgw. failed to start rgw: Failed to complete rgw: signal: aborted (core dumped)

This makes the service unavailable for some seconds until the service is restarted. Can anybody provide insights on this? I am running:

ceph version af31b0aa0 (5af31b0aa028c6a69306c890f8d91fb9463a28f7) luminous (stable)

Thank you!