pg_basebackup fails on inactive slave

pg_basebackup -w -U replication -h 127.0.0.1 -p 5432\
        -D /mnt/basebackups_last/  -F p -l "backup_24.02.2015" -x

I got message:
pg_basebackup: could not get transaction log end position from server: FATAL:  could not find any WAL files

-x - will by default take WALs on end of basebackup.

Is it normal because database master/slave aren't all that active at a time of taking this

basebackup that basebackup on slave fail with this message?

Should I remove "-x" option, it's not strictly needed because I have a service that is fetching

wals that can be combined with basebackups?

Thanks

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