Failed to compile.

./my-theme/index.less (./node_modules/css-loader??ref--10-oneOf-3-1!./node_modules/postcss-loader/src??ref--10-oneOf-3-2!./node_modules/less-loader/dist/cjs.js??ref--10-oneOf-3-3!./my-theme/index.less)
Module build failed (from ./node_modules/less-loader/dist/cjs.js):
Error: Cannot find module 'less'
    at Function.Module._resolveFilename (module.js:547:15)
    at Function.Module._load (module.js:474:25)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/Users/myusername/myapp/node_modules/less-loader/dist/index.js:8:36)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/Users/myusername/myapp/node_modules/less-loader/dist/cjs.js:3:18)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)