Mathematics achievement in different education systems around the world is assessed periodically in the Programme for International Student Assessment (PISA). PISA is deemed to yield robust international comparisons of mathematical attainment that enable individual countries and regions to monitor the performance of their education systems relative to standards being achieved internationally, with a view to informing their mathematics education policy decisions. Initially, the role of PISA in instigating mathematics education policy borrowing is outlined using England as a case study, and some existing technical critiques of PISA are then reviewed. Following this, aspects of Ludwig Wittgenstein's later philosophy of mind are used to reason that an over-reliance on the use of PISA to inform policy decisions in mathematics education may be problematic. It is suggested that, when PISA is viewed through a later Wittgensteinian lens, a potential deficiency in the underpinning psychometric model, pertaining to the inherent indeterminism in unmeasured mathematical abilities, may weaken PISA's utility in guiding mathematics education policy decisions. It is concluded that, whilst PISA mathematics scores may give some indication of the mathematical proficiency of a nation's students, caution is required before mathematics education policies are borrowed from other jurisdictions on the basis of PISA performance. Implications for the other PISA domains are also outlined.