diff --git a/zproject/prod_settings_template.py b/zproject/prod_settings_template.py
index 6da068e1ac..20acacf72c 100644
--- a/zproject/prod_settings_template.py
+++ b/zproject/prod_settings_template.py
@@ -168,6 +168,10 @@ AUTHENTICATION_BACKENDS = (
 # subdomain; if you're using this setting, the "Callback URL" should be e.g.:
 #   https://auth.zulip.example.com/complete/github/
 #
+# If you end up using a subdomain other then the default
+# recommendation, you must also set the 'ROOT_SUBDOMAIN_ALIASES' list
+# to include this subdomain.
+#
 #SOCIAL_AUTH_SUBDOMAIN = 'auth'
 
 ########
diff --git a/zproject/settings.py b/zproject/settings.py
index 6ee04c0619..489fd24593 100644
--- a/zproject/settings.py
+++ b/zproject/settings.py
@@ -355,7 +355,8 @@ DEFAULT_SETTINGS.update({
     'EMAIL_DELIVERER_DISABLED': False,
 
     # What domains to treat like the root domain
-    'ROOT_SUBDOMAIN_ALIASES': ["www"],
+    # "auth" is by default a reserved subdomain for the use by python-social-auth.
+    'ROOT_SUBDOMAIN_ALIASES': ["www", "auth"],
     # Whether the root domain is a landing page or can host a realm.
     'ROOT_DOMAIN_LANDING_PAGE': False,