In a recent paper, Joo et al. report from density functional theory calculations that H2 adsorption in MOF-5 lead to a contraction of the metal-organic framework's unit cell. The authors contrast that finding with "the intuition that gas adsorption in a confined system (e.g., pores in a material) increases internal pressures and then leads to volumetric expansion", and describe the contraction as extraordinary. We would like to point out in this comment that adsorption-induced contraction of microporous materials is actually a very generic phenomenon, which has been demonstrated experimentally in a large range of microporous materials and explained theoretically. At the same time, we would like to acknowledge that the authors should be credited for demonstrating this effect on the MOF-5 framework and characterizing its extent (of the order of 1% in volume). This is not atypical, if somewhat large, for inorganic microporous materials like zeolites, but small compared to metal-organic frameworks that show adsorption-induced structural transitions, such as the "breathing" MIL-53 (∆V/V ~ 40%).