Trying to add a border to my model, but modifier being weird

[WonderfulWafflez]

So I’m trying to make a cell shaded donut (i"m followed a tutorial on cell shading and i’m trying to apply that to my donut) And when I add in a solidify modifier this happens:

I think it’s because I already applied a solidify modifier when I modeled the donut originally.

[joseph]

Invert your thickness, i.e. turn it to a negative value