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The released ISO 26262 standard for automotive systems requires breaking down safety goals from the hazard analysis and risk assessment into functional safety requirements in the functional safety concept. It has to be justified that the defined functional safety requirements are suitable to achieve the stated safety goals. In this paper, we present a systematic, structured and model-based method to define functional safety requirements using a given set of safety goals. The rationale for safety goal achievement, the relevant attributes of the functional safety requirements, and their relationships are represented by a UML notation extended with stereotypes. The UML model enables a rigorous validation of several constraints expressed in OCL. We illustrate our method using an example electronic steering column lock system.