Shaping mould (1) for manufacturing sleepers with inserts (2) each consisting of an anchoring part (3) to be anchored in the sleeper body and a shoe part (4) projecting from the sleeper body, in which the bottom (10) of the shaping mould comprises elastically deformable sealing elements (5) each comprising a recess for sealingly accommodating the shoe part while the anchoring part projects from the bottom into the shaping mould, and in which holding means are present at the position of each opening for holding the insert in the shaping mould, characterized in that the holding means comprising clamping parts (6) with a shape which is adapted to the shoe part, and in that at least two rigid positioning stops (7, 8) are provided for the shoe part, in which the clamping parts pull an insert against the positioning stops, by which the correct position of the insert is ensured.