HAProxy restrict single backend by ip range

I have inherited an HAProxy setup with around twenty backend definitions (and little else) in the config file. I have been asked to restrict one of the backends to a specific IP range, but so far my research (and limited HAProxy knowledge) have yielded nothing.

Whilst reading the manual, I have found a network_allowed parameter that would work for a frontend, but I don't seem to have any front end definitions and I don't want to apply this restriction to any of the other proxy routes. Is there anything I can specifically use on a backend to restrict access by IP range?

Thanks,Simon