The only reason I ask is because that's always how, historically, I've always used that phrase (i.e. with the singular).

I did a quick google and afaict, there's basically no hard and fast rule:

http://english.stackexchange.com/questions/29843/types-of-followed-by-singular-or-plural

unless you're super strongly against this can we leave it, just because it's how I would write/say it - so it's less painful for me to read..! :smile: 

Thanks for your PR, btw :+1: