microbundle: regeneratorRuntime is not defined when using generator

{
  "name": "out",
  "source": "index.js",
  "dependencies": {
    "microbundle": "^0.12.3"
  }
}

function *hello() {
    return 42
}

console.log(hello())

running

$ yarn
$ yarn microbundle
$ node node dist/out.js

Results in this error

/Users/dominik/Code/microbundle-async/dist/out.js:1
var r=regeneratorRuntime.mark(e);function e(){return regeneratorRuntime.wrap(function(r){for(;;)switch(r.prev=r.next){case 0:return r.abrupt("return",42);case 1:case"end":return r.stop()}},r)}console.log(e());
      ^

ReferenceError: regeneratorRuntime is not defined
    at Object.<anonymous> (/Users/dominik/Code/microbundle-async/dist/out.js:1:7)
    at Module._compile (internal/modules/cjs/loader.js:1251:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1272:10)
    at Module.load (internal/modules/cjs/loader.js:1100:32)
    at Function.Module._load (internal/modules/cjs/loader.js:962:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47

It works if I add import 'regenerator-runtime/runtime'; to the top of the js file but it would be great if I didn’t have to guess that this extra import is required (and it won’t be required in the modern build for example: node dist/out.modern.js works).