Error without fields attibute in UpdateView

eturn handler(request, *args, **kwargs)
  File "/home/bgarcial/.virtualenvs/ihost/lib/python3.5/site-packages/django/views/generic/edit.py", line 236, in get
    return super(BaseUpdateView, self).get(request, *args, **kwargs)
  File "/home/bgarcial/.virtualenvs/ihost/lib/python3.5/site-packages/django/views/generic/edit.py", line 174, in get
    return self.render_to_response(self.get_context_data())
  File "/home/bgarcial/workspace/ihost_project/accounts/views.py", line 139, in get_context_data
    context = super(AccountProfilesView, self).get_context_data(**kwargs)
  File "/home/bgarcial/.virtualenvs/ihost/lib/python3.5/site-packages/django/views/generic/edit.py", line 93, in get_context_data
    kwargs['form'] = self.get_form()
  File "/home/bgarcial/.virtualenvs/ihost/lib/python3.5/site-packages/django/views/generic/edit.py", line 44, in get_form
    form_class = self.get_form_class()
  File "/home/bgarcial/.virtualenvs/ihost/lib/python3.5/site-packages/django/views/generic/edit.py", line 129, in get_form_class
    "the 'fields' attribute is prohibited." % self.__class__.__name__
django.core.exceptions.ImproperlyConfigured: Using ModelFormMixin (base class of AccountProfilesView) without the 'fields' attribute is prohibited.
[04/Apr/2017 00:28:03] "GET /accounts/profile/david/ HTTP/1.1" 500 112864