bdr admin role

This doc specifies to initdb with the admin user "postgres,"
http://bdr-project.org/docs/stable/quickstart-instances.html
but if I do that the supervisor falls over with:
$ cat bdr5598.log
LOG: registering background worker "bdr supervisor"
LOG: database system was shut down at 2015-09-02 16:04:45 EDT
LOG: starting up replication identifier with ckpt at 0/171EBF8
LOG: MultiXact member wraparound protections are now enabled
LOG: starting background worker process "bdr supervisor"
LOG: autovacuum launcher started
LOG: database system is ready to accept connections
LOG: Created database bdr_supervisordb (oid=16384) during BDR startup
LOG: worker process: bdr supervisor (PID 21666) exited with exit code 1
FATAL: role "postgresql" does not exist
LOG: starting background worker process "bdr supervisor"

It works if I init with "-U postgresql"