Filed my 2017 returns a year later in 2018. Should the refund be reported on 2018 or 2019 return?

Hello,

I was very late in filing my 2017 returns (filed in April 2018, a year later). I haven't filed my 2018 returns yet and would like to know whether the refund from 2017 should be reported on my 2018 return (even though the funds were received in 2019), or on 2019 return next year.

Thanks!