Can't access content_for defined in component

[Hans Lemuet]

I'm trying to set a content_for in a component, and then access it in my layout:

/ frontend/components/admin/form/items/_items.html.slim

.admin-form-items
  / [...]
  - content_for :after_wrapper do
    .test Hello World

/ app/views/layouts/admin.html.slim

doctype html
html
  head
    / [...]

  body.is-admin
    = c "admin/header"
    = yield
    = yield :after_wrapper

But nothing gets yielded in the layout. Any idea?