A foldable stroller frame having right and left front, right and left rear legs, and right and left handle supports joined at a right and left folding joints in a manner permitting folding movement about a folding axis between deployed and folded positions. A seat panel connects the front legs and includes a movable portion being movable between first and second positions. A seat back frame is connected to the movable portion at a seat back pivot. Spacing between the seat back pivot and the folding axis is dependent upon the position of the movable portion. When in the first position, the spacing is greatest and precludes frame folding due to interference between the seat back frame and a transverse element between the handle supports. When in the second position, spacing is minimized and frame folding is permissible without interference between the seat back frame and the transverse element.