During learning, humans recruit multiple cognitive mechanisms, including value-based reinforcement learning and ex-ecutive functions, like working memory. Recent research has begun to unmask connections between these two systems,proposing roles for attention and working memory in shaping underlying learning computations. Here, using a simpleinstrumental learning task, we provide evidence that working memory plays a role in establishing the correct state spacethat reinforcement learning operates over. We show that reinforcement learning is impaired when executive functioning istaxed by a secondary task and that this effect is especially pronounced when the two tasks are performed simultaneouslyrather than alternated. Computational modeling suggests that when the executive function is occupied, the reinforcementlearning system forms policy over a confused state-space. This study adds to a growing body of research proposing a morefundamental role for high-level executive processes in low-level reinforcement learning computations.