Pericentric heterochromatin is marked by heterochromatin protein 1 (HP1), which is recruited to these regions by trimethylated Lys9 of histone H3 (H3K9me3); however it has been suggested that this modification is not the sole requirement for stable HP1 enrichment. In this study, Romeo et al. show in mouse cells that the SUMO protease SENP7 contains a double PXVXL (Pro-X-Val-X-Leu) motif module that mediates its interaction with HP1, independent of its ability to de-SUMOylate HP1. Furthermore, they report that this interaction motif maintains HP1 accumulation at pericentric domains and restricts HP1 mobility. On the basis of their findings, the authors propose a model whereby the SENP7 module locks several HP1 molecules to H3K9me3-modified nucleosomes.