Abstract: A case for an electronic device such as a head-mounted device may have a main housing portion that separates an interior region from a surrounding exterior region. The main housing portion may have an opening through which the head-mounted device is received into the interior region. Flexible protruding portions of the main housing portion may form a flexible tab and a flexible flap. To make size adjustments to the interior region, the flexible tab may slide within an opening in a cover. The cover may be configured to move between an open position in which the opening is uncovered and a closed position in which the head-mounted device is enclosed within the interior region by the main housing portion and the cover. Deformable protrusions in the case may be used to seal openings in the head-mounted device when the device is in the interior region.