The invention relates to an assembly for securing a slide-in unit in a mounting cage of a computer system. The mounting cage has a first side panel and a second side panel opposite the first side panel. The first side panel has at least one engagement element for engaging into a lateral fastening opening of the slide-in unit. The first side panel and the second side panel are arranged at a distance to one another such that the slide-in unit can be inserted into the mounting cage past the engagement element. After the insertion, a fastening element secured to the second side panel cooperates with the slide-in unit in such a way that the slide-in unit is pushed in the direction of the first side panel and the engagement element engages in the respective lateral fastening opening of the slide-in unit.