State the one you want, not the one you're currently making. They won't (and legally should't be able to) check.
And if they do and somehow, your previous employer disclosed this to them (a big no no), you can always say "I was underpaid then and what I was making there is not relevant to the position I'm applying to with your right now. I also think I've learned a lot in my past position, which justifies this jump in compensation".
And if they do and somehow, your previous employer disclosed this to them (a big no no), you can always say "I was underpaid then and what I was making there is not relevant to the position I'm applying to with your right now. I also think I've learned a lot in my past position, which justifies this jump in compensation".