Can't sendAction from event handler triggered by component

I've got a component sending an action:

this.sendAction('action', data.files)

In the template I used the component like this

{{file-upload url="api/v1/upload" action="finishedUpload"}}

In the controller handling the event I'd like to send another action (to the same controller but I get the infamous TypeError: undefined is not a function

finishedUpload: function(files) {
  this.sendAction('insertImage')
}

How can I get the context of the current controller so I can send actions in the event-handler?