Certification for sustainable biofuels has been developed to ensure that biofuel production methods adhere to social and environmental sustainability standards. As such, requiring biofuels to be certified has become part of policy documents such as the EU Renewable Energy Directive (RED) that aim to promote energy security, reduce emissions and promote rural development. According to the EU RED, in 2020 10% of our transport energy should come from renewable sources, including biofuels. Only certified biofuels may count towards this target. In this paper I examine what biofuel certificates are, what they can do and what their weak points are. I argue that the EU RED makes an important but unjustified assumption in demanding certified biofuels for its target: that if biofuel production is sustainable, then biofuel use is too. Applying the use plan approach from the philosophy of technology to biofuel certification, I show why this assumption is unjustified and why the EU is in fact making "improper use" of biofuel certification. Finally, I discuss ways in which biofuel certification could be used in working towards the EU RED's goals.