A key mechanism is disclosed. The key mechanism comprises a keycap, a dome support structure positioned relative to the keycap and defining an opening, an actuation mechanism coupled to the keycap, and a collapsible dome positioned in the opening of the dome support structure. The actuation mechanism is configured to movably support the keycap relative to the dome support structure. The dome comprises an upstop member configured to limit upward travel of the collapsible dome.