views.py

from django.views.defaults import page_not_found as django_page_not_found
from django.views.decorators.csrf import requires_csrf_token
from django.views.defaults import ERROR_404_TEMPLATE_NAME

@requires_csrf_token
def page_not_found(request, exception, template_name=ERROR_404_TEMPLATE_NAME):
    path = request.path.strip("/")
    # custom logic goes here
    
    # see if there's a lowercase match
    if request.path != request.path.lower():
        try:
            view, args, kwargs = resolve(request.path.lower())
            view(*args, **kwargs)
            return http.HttpResponseRedirect(request.path.lower())
        except Exception:
            # do nothing so we return the original exception
            pass
    return django_page_not_found(request, exception, template_name=template_name)