Stack overflow when inheriting from base (master) template

I want to extend access_control block to add authentication menu links. I don't want to overwrite whole master.html template, so I created templates/admin/mymaster.html file with the following contents:

{% extends 'admin/master.html' %}
{% block access_control %}
    {{ super() }}
        <ul class="nav navbar-nav navbar-right">
            <...>
        </ul>
{% endblock %}

Now I've got: What am I doing wrong? Lately, I've overridden admin/index.html same way:

{% extends 'admin/master.html' %}
{% block body %}
  <p>Here I'm going to display some data.</p>
{% endblock %}

and it works well.