Research suggests that in-store crowding can lower customers’ spending, thus limiting overall benefits of high store frequentation. Here, we propose that this negative effect can be mitigated by adjusting store ambiance, specifically by using certain types of in-store music. To test this idea, we conducted a longitudinal field experiment in which we manipulated in-store music tempo and measured social density in six European retail stores. Analyzing over 40,000 individual shopping baskets, we found that social density had an inverted u-shape effect on customer spending. This effect was moderated by in-store music tempo, such that fast music strongly increased spending under high-density conditions. The increase in shopping basket value was driven by customers buying more items rather than buying items that were more expensive. Fast music thus alleviated negative effects of social density. We discuss the theoretical implications of these findings and describe how practitioners can use in-store music to counter negative effects of high customer density.