diff --git a/app/auth/routes.py b/app/auth/routes.py
index b3c3651a..5391a9e2 100644
--- a/app/auth/routes.py
+++ b/app/auth/routes.py
@@ -9,7 +9,7 @@ from wtforms import Label
 from app import db, cache
 from app.auth import bp
 from app.auth.forms import LoginForm, RegistrationForm, ResetPasswordRequestForm, ResetPasswordForm
-from app.auth.util import random_token, normalize_utf, ip2location
+from app.auth.util import random_token, normalize_utf, ip2location, no_admins_logged_in_recently
 from app.email import send_verification_email, send_password_reset_email
 from app.models import User, utcnow, IpBan, UserRegistration, Notification, Site
 from app.utils import render_template, ip_address, user_ip_banned, user_cookie_banned, banned_ip_addresses, \
@@ -91,6 +91,11 @@ def register():
     disallowed_usernames = ['admin']
     if current_user.is_authenticated:
         return redirect(url_for('main.index'))
+
+    # Abandoned open instances automatically close registrations after one week
+    if g.site.registration_mode == 'Open' and no_admins_logged_in_recently():
+        g.site.registration_mode = 'Closed'
+
     form = RegistrationForm()
     # Recaptcha is optional
     if not current_app.config['RECAPTCHA_PUBLIC_KEY'] or not current_app.config['RECAPTCHA_PRIVATE_KEY']:
diff --git a/app/auth/util.py b/app/auth/util.py
index 851e7777..9f5c0272 100644
--- a/app/auth/util.py
+++ b/app/auth/util.py
@@ -1,9 +1,11 @@
 import random
+from datetime import timedelta
 from unicodedata import normalize
 
 from flask import current_app
 
 from app import cache
+from app.models import Site, utcnow
 from app.utils import get_request
 
 
@@ -41,3 +43,16 @@ def ip2location(ip: str):
         postal = ''
     return {'city': data['city'], 'region': data['region'], 'country': data['country'], 'postal': postal,
             'timezone': data['timezone']}
+
+
+def no_admins_logged_in_recently():
+    a_week_ago = utcnow() - timedelta(days=7)
+    for user in Site.admins():
+        if user.last_seen > a_week_ago:
+            return False
+
+    for user in Site.staff():
+        if user.last_seen > a_week_ago:
+            return False
+
+    return True