Error using blocks at Nunjucks

Am I able to insert blocks inside a set element with Nunjucks? Like this:

        {% set css %}
        {% block includeCSS %}
            {% include "styles.css" %}
        {% endblock %}
        {% endset %}

        {% set js %}
        {% block includeJS %}
            {% include "script.js" %}
        {% endblock %}
        {% endset %}

When I’m running this file:

{% extends 'layouts/default.njk' %}
{% block includeCSS %}CONTENT{% endblock %}

I’m getting an error:

Template render error: (./src/_includes/layouts/default.njk)
      Error: unknown block "includeJS"

I basically need to have all blocks inside the child template, is there any way to avoid this?