The present application relates to a pump unit (101; 201; 201') for a fuel injection system. The pump unit (101; 201; 201') has an inlet valve (107; 207), an outlet valve (109; 209), a supply line (111; 211) for supplying fuel, a pumping chamber (105; 205; 205'), and a plunger (119; 217; 217') for pressurising fuel in the pumping chamber (105; 205; 205'). The inlet valve (107; 207) comprising an inlet valve member (113; 221; 221') movable between a first position and a second position. The inlet valve member (113; 221; 221') has an aperture (117; 229) formed therein. The aperture (117; 229) provides a first fluid pathway between the pumping chamber (105; 205; 205') and the supply line (111; 211) when the inlet valve member (113; 221; 221') is in its first position, and the aperture (117; 229) provides a second fluid pathway between the pumping chamber (105; 205; 205') and the outlet valve when the inlet valve member is in its second position.