[Exim] option "transport_filter" unknown

I am trying to use a transport_filter in Exim 4.12, but exim -v gives:
LOG: PANIC DIE
Exim configuration error in line 382:
option "transport_filter" unknown

Lines 382 and thereabouts are:

smart_route:
    driver = manualroute
    domains = !+local_domains
    transport_filter = /usr/local/bin/myfilter
    transport = remote_smtp
    route_list = * 193.109.254.3

Am I missing something?

Lawrence