A method for manufacturing a turbine-engine blade from a preform made from polymerized composite material in a mold comprising a bottom part and a top part, comprising at least one closure step during which the top part of said mold is attached to the bottom part of the mold containing the preform, wherein it comprises, prior to said closure step, at least one insertion substep during which a first end of an immobilization element is inserted in a bottom part of the preform in a substantially transverse direction, and a positioning substep during which a second, opposite end of said element is disposed in a complementary reception cavity emerging in the bottom part of the mold.