USP14 is a proteasome-associated deubiquitinating (DUB) enzyme which can inhibit the degradation of ubiquitin–protein conjugates both in vitro and in cells. This compound is a cellpermeable USP14 inhibitor which leads to increased proteasome activity. Enhancement of proteasome activity through inhibition of USP14 may offer a strategy to reduce the levels of aberrant proteins in cells under proteotoxic stress.