Enumerating an expanded bus system in a system. The expanded bus system may include a first bus, a bridge coupled to the first bus, and a second bus coupled to the bridge, where the second bus includes one or more downstream bus ports. One or more of the downstream bus ports may initially be masked. An initial bus enumeration may be performed during system boot, which may not include enumerating the masked bus ports. After the initial bus enumeration, the masked bus ports may be unmasked. An operating system may re-enumerate the bus system, which may include enumerating the no-longer-masked bus ports.