Abstract: The invention relates to an improved arrangement of an air pump which can be inserted into the seat pillar (50) of a bicycle and which comprises a cylinder (2), a piston with a piston rod (3), a handle (4) and an air outlet valve (5) which is displaceably connected to the cylinder (2). According to the invention, a deformable element (6) is provided between the cylinder (2) and the air outlet valve (5), the diameter (d) thereof being able to be increased by flipping over the air outlet valve (5) such that the longitudinal axis (A) of the cylinder (2) and the longitudinal axis (a) of the air outlet valve extend in an at least substantially parallel manner. The air pump (1) can be blocked in the seat pillar (50).