Package managers usually only deal with packages and their versions, and the con-straints on their dependencies towards other packages' versions. Among package man-agers, opam is probably the first one to introduce the notion of switch, i.e. the ability to manage different directories, where different sets of packages with different versions are installed, as each directory is treated as an independant universe when solving depen-dency constraints. In this talk, we will support a case to be able, in opam, to manage different switches in the same universe, allowing to express dependency constraints that cross switch boundaries.