Stable single mode operation of distributed feedback quantum cascade lasers operating in room-temperature continuous-wave mode is reported. Feedback is provided by the second-order grating in a both index- and loss-dominated coupling scheme. Reliable single mode emission at lambda similar to 4.7 mu m with a side-mode suppression ratio similar to 30 dB is observed. A linear tuning of wavelength with heat-sink temperature or injection current indicates the stable single mode operation without mode hopping. (C) 2014 Elsevier Ltd. All rights reserved.