The paper analyses the inclusion of unilateral safe harbours as a reportable hallmark under Directive on Administrative Cooperation (DAC) 6. There is uncertainty regarding the scope of this hallmark on the definition of safe harbours and whether internationally accepted safe harbours should be reported. This article addresses these open issues and analyses the conformity of this hallmark with EU primary law and with the objective and purpose of DAC 6. It also discusses whether the inclusion of such a hallmark imposes an unreasonable burden on taxpayers and intermediaries that undermines the objectives of safe harbour rules to achieve simplicity and tax certainty.