We present a T-shaped waveguide for a quantum-wire intersubband laser in the GaAs/AlGaAs heterosystem for the midinfrared spectral region around 8 mu m. Such a device is fabricated using the cleaved edge overgrowth (CEO) technique. The suggested waveguide structure is compatible to this growth technique. The confinement factor and the waveguide losses due to free carrier absorption are calculated solving the scalar wave equation and compared to the results for a conventional quantum cascade laser (QCL) in the GaAs/AlGaAs material system based on coupled quantum-wells. We show that the optical mode can be confined near the active region of a quantum-wire cascade structure with the presented T-shaped waveguide design. Simultaneously the waveguide losses can be reduced compared to a conventional QCL waveguide design. However, the confinement factor is substantially reduced as a result of a small optically active region in the quantum-wire cascade device.