A round baler is disclosed having a bale forming chamber. A duck bill, which comprises a pair of elongate plates that are biased towards one another to grip the wrapping material between them, is movable between an advanced position and a retracted position to introduce the free end of a wrapping material drawn from a supply roll into the bale forming chamber of the baler. A cutting device is located between the retracted position of the duck bill and the bale forming position for severing the length of wrapping material wrapped around the bale in the bale forming chamber at the end of a bale wrapping cycle from the supply roll. In the invention, a clamping device is provided to apply an additional force to urge the plates of the duck bill towards one another while the duck bill is in the retracted position in order for the wrapping material to be gripped more firmly between the plates of the duck bill between bale wrapping cycles.