A Roots-type blower comprising: - a housing defining first and second transversely overlapping cylindrical chambers (41, 42), said housing comprising a first end wall and a second end wall, said housing defining at least one inlet port comprised in said first end wall and at least one outlet port is formed at an intersection of the first and second chambers (41, 42), adjacent said second end wall; - first and second meshed, lobed rotors (31, 32) disposed, respectively, in said first and second cylindrical chambers (41, 42); each rotor including a plurality N of lobes (51, 52), each lobe having first and second axially facing end surfaces sealingly cooperating with said first and second end walls (43, 44), respectively, and a top land (53, 54) sealingly cooperating with said cylindrical chambers (41, 42), each lobe (51, 52) having its first and second axially facing end surfaces (61, 62) defining a twist angle of at least 90°, and each lobe (51, 52) defining a helix angle; - a plurality of control volumes for transfer of fluid from the at least one inlet port to the at least one outlet port, 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), first end wall, and/or second end wall; and - a leakage mechanism for effecting a leakage of fluid between adjacent control volumes, said leakage mechanism including blowholes formed within the cylindrical chambers (41, 42) in connection with meshing of the lobes (51, 52) of the first and second rotors (31, 32); characterized in that the Roots-type blower comprises an additional leakage mechanism in form of at least two individual backflow slots provided on each side of a centre line, each backflow slot extending through the housing wall of each cylindrical chamber (41, 42) for effecting a leakage of fluid from downstream the at least one outlet port into a control volume prior to traversal of the at least one outlet port boundaries by the top land (53, 54) of the lead lobe (51, 52) of said control volume, wherein the individual backflow slots on either side of the centre line are arranged along a slot axis having a slot axis angle (α) to the longitudinal direction of the housing, wherein said slot axis angle (α) is smaller than the helix angle of the lobes (51, 52), such that the individual backflow slots along each slot axis sequentially enables a fluid flow passage to the control volume as the top land (53, 54) of the lead lobe (51, 52) of the control volume progressively traverses the slot axis. - a housing defining first and second transversely overlapping cylindrical chambers (41, 42), said housing comprising a first end wall and a second end wall, said housing defining at least one inlet port comprised in said first end wall and at least one outlet port is formed at an intersection of the first and second chambers (41, 42), adjacent said second end wall; - first and second meshed, lobed rotors (31, 32) disposed, respectively, in said first and second cylindrical chambers (41, 42); each rotor including a plurality N of lobes (51, 52), each lobe having first and second axially facing end surfaces sealingly cooperating with said first and second end walls (43, 44), respectively, and a top land (53, 54) sealingly cooperating with said cylindrical chambers (41, 42), each lobe (51, 52) having its first and second axially facing end surfaces (61, 62) defining a twist angle of at least 90°, and each lobe (51, 52) defining a helix angle; - a plurality of control volumes for transfer of fluid from the at least one inlet port to the at least one outlet port, 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), first end wall, and/or second end wall; and - a leakage mechanism for effecting a leakage of fluid between adjacent control volumes, said leakage mechanism including blowholes formed within the cylindrical chambers (41, 42) in connection with meshing of the lobes (51, 52) of the first and second rotors (31, 32);