In this paper, we explore the impact of part-time work on firm productivity. Using a large panel data set of Italian corporations' balance sheets for the period 2000-2010, we first estimate the total factor productivity (TFP) of each firm for each year. We use different approaches aimed at solving input simultaneity, including a version of Ackerberg et al.'s (2006) control function approach, which accounts for firm fixed effects. We then match the TFP estimates with rich information on the firms' use of part-time work obtained from survey data and estimate the impact of part-time work on TFP at the firm level. We find that an increase of 1 standard deviation in the part-time share reduces TFP by 2.03%. The results suggest that this harmful effect stems from horizontal rather than vertical part-time arrangements. We also find that firms declaring that they use part-time work to accommodate workers' requests suffer the most. Moreover, we show that the so-called 'flexible' and 'elastic' clauses are successful in reducing the negative impact associated with part-time work.