Postcapitalist commons are a growing area of interest in the efforts to generate alternatives to capitalism in the present. Commons are understood as self-organised collectives based around shared resources; yet postcapitalist commons have an additional element, in operating within while projecting an “after” capitalism. This can give rise to tensions since commons striving for postcapitalism also require a certain amount of capital to survive and function within capitalism. FairCoop is a radical postcapitalist commons that adopted the cryptocurrency FairCoin in 2014. FairCoop, through FairCoin, was able to generate some trans-local connections through its use of peer2peer technologies and was thus able to scale-up. Its design, however, was ultimately unsustainable due to insufficiently clear boundaries from capital. After highlighting the lack of commons boundaries around FairCoop, we identify some additional commons-capital boundary design principles which could contribute to the sustainability of future postcapitalist commons experiments that are seeking to scale.