A fiber preform for a turbine engine blade and a single-piece blade suitable for being made by means of such a preform, a bladed wheel, and a turbine engine including such a blade; the fiber preform obtained by three-dimensional weaving comprises a first longitudinal segment (41) suitable for forming a blade root, a second longitudinal segment (42) extending the first longitudinal segment (41) upwards and suitable for forming an airfoil portion, a first transverse segment (51) extending transversely from the junction between the first and second longitudinal segments (41, 42), and suitable for forming a first platform; the first transverse segment (51) includes at least one non-interlinked portion comprising a top strip (51b) and a bottom strip (51a), and at least one insert (61) is arranged between the top and bottom strips (51b, 51a) of the non-interlinked portion of the first transverse segment (51).