max_prepared_foreign_transactions is unrecognized

["Eric J. Van der Velden" <ericjvandervelden@xxxxxxxxx>]

On https://wiki.postgresql.org/wiki/2PC_on_FDW it says I have to set the configuration parameter "max_prepared_foreign_transactions"  in postgresql.conf. When I restart postgres, I see:

LOG:  unrecognized configuration parameter "max_prepared_foreign_transactions" in file "/var/lib/postgresql/data/postgresql.conf" line 689

Thanks,

Eric.