During mitosis, the nuclear lamina is disassembled and then reassembled, which involves the reversible phosphorylation of lamin proteins. While mitotic kinases, such as Cdk1, have been shown to phosphorylate lamin A, its timely dephosphorylation is less well understood but has been suggested to involve protein phosphatase 1 (PP1). Takanobu Moriuchi and Fumiko Hirose previously demonstrated that dephosphorylation of lamin A requires its association with SUMO through a SUMO-interacting motif (SIM), and in this study (Moriuchi and Hirose, 2021), they now further investigate the role of SUMOylation in lamin A regulation. The authors show here that RepoMan, a regulatory subunit specific for PP1γ, is transiently SUMOylated during telophase and colocalises with lamin A on chromosomes. Deletion of RepoMan or expression of a SUMO mutant that is unable to interact with a SIM impairs lamin A dephosphorylation and reformation of the nuclear lamina, strongly suggesting that SUMOylated RepoMan recruits lamin A to mediate its dephosphorylation and that this is crucial for nuclear envelope reassembly. These data thus provide important new insights into the importance of SUMO–SIM interactions in mediating the spatiotemporal events that coordinate the completion of mitosis. Further studies will help to elucidate the enzymes that mediate the transient SUMOylation that is the basis of this regulation.