The question rnevius linked to fixed this for me. To add a bit more detail, I created a file mysite/account_adapter.py containing:
from allauth.account.adapter import DefaultAccountAdapter
class NoNewUsersAccountAdapter(DefaultAccountAdapter):
def is_open_for_signup(self, request):
"""
Checks whether or not the site is open for signups.
Next to simply returning True/False you can also intervene the
regular flow by raising an ImmediateHttpResponse
(Comment reproduced from the overridden method.)
"""
return False
And then added this to mysite/settings.py:
ACCOUNT_ADAPTER = 'mysite.account_adapter.NoNewUsersAccountAdapter'
