The invention concerns a Roots-type blower (1) comprising a housing (20) defining first and second transversely overlapping cylindrical chambers (41, 42) and at least one inlet port (23) and an outlet port (25); first and second meshed, lobed rotors (31, 32), each lobe having a top land (53, 54) sealingly cooperating with said cylindrical chambers (41, 42), a plurality of control volumes for transfer of fluid, each control volume being defined by a pair of adjacent lobes (51, 52) on one of the rotors (31, 32), and at least one of the cylindrical chambers (41, 42); and blowholes (55) formed within the cylindrical chambers (41, 42) in connection with meshing of the lobes (51, 52) of the first and second rotors (31, 32); wherein blower (1) comprises at least one backflow slot (29) extending through the housing (20) wall of each cylindrical chamber (41, 42) for effecting a leakage of fluid from downstream the at least one outlet port (25) into a control volume. The invention also concerns a Roots-type blower (1) comprising at least one bleed recess (45) provided in an end wall (44) of the cylindrical chambers (41, 42), wherein said bleed recess (45) provides a passage such that fluid is enabled to leak between adjacent control volumes.