Verification of a design for a multi-voltage circuit which defines a plurality of iso-voltage rail blocks, and which comprises voltage state information for the iso-voltage-rail blocks. Verification includes generating cross-over information regarding a cross-over signal between two iso-voltage-rail blocks, identifying the voltage state relationship between the two iso-voltage-rail blocks based on the voltage state information, and verifying the validity of the cross-over signal based on the determined voltage state relationship.