We report on the optical properties of m-plane GaInN/GaN quantum wells (QWs). We found that the emission energy of GaInN QWs grown on m-plane SiC is significantly lower than on nonpolar bulk GaN, which we attribute to the high density of stacking faults. Temperature and power dependent photoluminescence reveals that the GaInN QWs on SiC have almost as large internal quantum efficiencies as on bulk GaN despite the much higher defect density. Our results indicate that quantum-wire-like features formed by stacking faults intersecting the quantum wells provide a highly efficient light emission completely dominating the optical properties of the structures. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3607301]