A corrosion testing device comprising a coupon holder for a sucker rod of a pump system and at least one coupon for corrosion testing, wherein the coupon holder comprises a holder body having an outer body surface and an inner contact surface, which inner contact surface is placeable on an outer rod surface of the sucker rod and defines a longitudinal body axis of the holder body, the at least one coupon is attached to the holder body and positioned at the outer body surface and at a radial coupon distance from the longitudinal body axis, the outer body surface comprises at least one guiding surface part located at a radial surface distance from the longitudinal body axis, and the radial surface distance is larger than the radial coupon distance.