A turbomachine rotor disk including inter-blade platforms fixed to ribs delimited by cavities in which blade roots are retained, and protective liners mounted between the flanks of the cavities of the disk and the blade roots is disclosed. The protective liners have a C-shaped cross section so that they can be fitted translationally and retained radially on the ribs of the disk and constitute a locking device which locks the platforms on the ribs of the disk.