A firmware enumerates the buses of root bridges in the computing system. If an OOR condition occurs during enumeration of the buses, the firmware determines the number of required buses for each root bridge causing an OOR condition. The number of required buses for bridge devices connected to each root bridge causing an OOR condition can be identified using the same set of bus numbers. Once the firmware has determined the number of buses required by each root bridge, including those not causing an OOR condition, the firmware reallocates the number of available buses between the root bridges such that each root bridge is allocated a number of the available buses greater than or equal to the number of required buses. The firmware stores data identifying the allocation and restarts the computing device. Upon rebooting, the computing system utilizes the new allocation of bus numbers to eliminate the OOR condition.