I had a ONE briefly and recall the rear fender clearance was kinda tight. Not all tire profiles are created equal and you might bet stuck buying a tire, pulling the rear wheel, installing the new tire, re-installing just to see if it clears would be what I'd do if no one had a confirmed fit. What 20x3 tires are you considering? I installed tire liners on my ONE and the stock tires were tight on the rim, like almost bending my Pedro tire levers! So keep that in mind as well.
Spokewrench above did point out the rim width coming into the equation as well.