To discover novel factors involved in the final steps of 40S ribosomal subunit biogenesis in human cells, we isolated late cytoplasmic 40S subunit precursors by affinity purification (AP) of the assembly factor RIOK1. Subsequent analysis of their composition by mass spectrometry (MS) led to identification of the deubiquitinase USP16. AP-MS of USP16 confirms that it is a component of late cytoplasmic pre-40S particles and we further show that USP16 possesses a new, ribosome-associated function.