A tamper-resistant aerator including an aerator cartridge, an insert defining at least one removal slot, and a locking ring defining at least one removal slot at least partially disposed within a housing is disclosed. The locking ring rotates with respect to the housing to allow alignment of the removal slot of the locking ring with the removal slot of the insert. Alignment of the slots form a continuous passageway through the locking ring and into the insert. Alternatively, a plurality of removal slots may be provided. A mating engagement between the locking ring and the housing secures the locking ring within the housing while still allowing it to rotate with respect to the housing. An aerator system is also provided comprising an aerator as described above and a tool adapted to be received in the continuous passageway formed by the alignment of the slots and engage the insert.