A housing for a handheld computing device can include a metallic outer shell having a substantially flat base and a sidewall connected to a periphery of the base, the sidewall having a card slot, the outer shell having an inner surface and an outer surface, and a corrugated stiffener connected to the inner surface of the base and positioned adjacent to the card slot, the stiffener including a series of substantially parallel ridges and troughs and configured to provide rigidity to the housing.