Hayek's epistemic arguments against central planning and in defence of market economies have recently been redeployed by some market-socialists against more decentralized models of non-market socialism. This paper considers the cogency of these arguments through an examination of an unpublished exchange in the socialist calculation debates between Hayek and a proponent of non-market associational models of socialism, Otto Neurath. Contrary to the standard view of the debates, Neurath shared many of the assumptions of Hayek's epistemic arguments and similarly criticized technocratic models of planning. The paper outlines Neurath's defence of associational socialism from his early role in the Bavarian revolution through his engagement in the post-war housing movements in Vienna and the unity of science movement. While Neurath's response to Hayek is not entirely successful, his proposals for associational models of socialism point to problems not just in Hayek's criticisms of non-market socialism, but also those of more recent market-socialists.