Most errors in critical systems arise in the requirements. Consistency and completeness of such requirements as well as their traceability throughout the development are very important. However, it has been found that the current revision of IEC 61508:2010 does not require either requirement to be checked. We propose that clauses be added to IEC 61508 in the forthcoming maintenance cycle to require checking of safety requirements for consistency and relative completeness, along with a Technical Specification which indicates how this may be done using formal methods and available tools.