Boots with fit adjustment systems that are configured to selectively adjust a fit of the boot on the wearer's foot by engaging the foot with more force and/or across a greater surface area relative to a pull-on boot that lacks the fit adjustment system. The fit adjustment system may adjust the fit of the boot without adjusting the external dimensions of the boot. The fit adjustment system includes an instep pad that is positioned interior of the external surface of the upper within an instep region of the boot, a lace that is coupled to the instep pad, and a lace adjustment mechanism. The lace adjustment mechanism includes a lace lock that selectively defines an adjustment length of the lace. Actuating the lace adjustment mechanism to reduce the adjustment length exerts a tightening force on the instep pad and draws the instep pad toward a heel region of the boot.