Corrugated paperboard box blanks are formed with corner fold lines defined by a colinear slit and score. The score deflects one slit edge of the liner out of the plane of the blank such that, when a subsequent lateral fold is made on the line, one slit edge tucks consistently under the other along the full length of the fold line. The resultant box blanks fold more squarely than prior art folded boxes with no significant loss in the compressive strength of the box.