Pug's `doctype` option is set to `html` by default in [pug-plain-loader](https://github.com/yyx990803/pug-plain-loader#options). The reasoning is also explained there: > The doctype option is set to html by default, since most Vue templates are HTML fragments without explicit doctype. The same we should do here in `component-compiler-utils` (otherwise developers should figure it out and set it by themesevles https://github.com/vuejs/vue-jest/issues/170) I can create a PR if we agree to do it