Custom templatetags in overridden django-allauth template

Question

I am using django-allauth with a custom signup template based on the default. Is there a way to include custom template tags in the template? using {% load custom_tags %} gives me a TemplateSyntaxError: custom_tags is not a registered tag library. Must be one of:. Here is my code:

templates/account/signup.html

(overrides allauth default)

{% extends "account/base_entrance.html" %}
{% load allauth i18n %}
{% load custom_tags %}
{% block head_title %}
    {% trans "Sign Up" %}
{% endblock head_title %}
{% block content %}
    {% element h1 %}
        {% trans "Sign Up" %}
    {% endelement %}
    <p>
        {% blocktrans %}Already have an account? Thsen please <a href="{{ login_url }}">sign in</a>.{% endblocktrans %}
    </p>
    {% url 'account_signup' as action_url %}
    {% element form form=form method="post" action=action_url tags="entrance,signup" %}
        {% slot body %}
            {% csrf_token %}
            {% element fields form=form unlabeled=True %}
            {% endelement %}
            {% if redirect_field_value %}
                <input type="hidden"
                       name="{{ redirect_field_name }}"
                       value="{{ redirect_field_value }}" />
            {% endif %}
        {% endslot %}
        {% slot actions %}
            {% element button tags="prominent,signup" type="submit" %}
                {% trans "Sign Up" %}
            {% endelement %}
        {% endslot %}
    {% endelement %}
    {% if SOCIALACCOUNT_ENABLED %}
        {% include "socialaccount/snippets/login.html" with page_layout="entrance" %}
    {% endif %}
{% endblock content %}

tempalatetags/custom_tags.py

from django import template
from django.http import HttpRequest

register = template.Library()

# A test tag.
@register.simple_tag(takes_context=True)
def tag(context):
    return context['request']['address']