This document revises the RFC 3775 rules on how Alternate Care-of Address option is processed. Alternate Care-of Address option is used to carry the current care-of address inside a Mobility Header message. This is used in addition to the source address in the packet in order to ensure that the care-of address is protected by IPsec ESP, the security mechanism that protects Mobility Header messages. Unfortunately, RFC 3775 did not require verification that the source address and care-of address are the same. This document adds that requirement.