diff --git a/app/javascript/packs/admin.jsx b/app/javascript/packs/admin.jsx
index ebcc6903f8c0f0..524b6a5c461aa6 100644
--- a/app/javascript/packs/admin.jsx
+++ b/app/javascript/packs/admin.jsx
@@ -145,6 +145,10 @@ delegate(document, '#form_admin_settings_enable_bootstrap_timeline_accounts', 'c
 const onChangeRegistrationMode = (target) => {
   const enabled = target.value === 'approved';
 
+  [].forEach.call(document.querySelectorAll('.form_admin_settings_registrations_mode .warning-hint'), (warning_hint) => {
+    warning_hint.style.display = target.value === 'open' ? 'inline' : 'none';
+  });
+
   [].forEach.call(document.querySelectorAll('#form_admin_settings_require_invite_text'), (input) => {
     input.disabled = !enabled;
     if (enabled) {
diff --git a/app/views/admin/settings/registrations/show.html.haml b/app/views/admin/settings/registrations/show.html.haml
index 168f1097570772..4ece27bf4e708f 100644
--- a/app/views/admin/settings/registrations/show.html.haml
+++ b/app/views/admin/settings/registrations/show.html.haml
@@ -10,9 +10,11 @@
 
   %p.lead= t('admin.settings.registrations.preamble')
 
+  .flash-message= t('admin.settings.registrations.moderation_recommandation')
+
   .fields-row
     .fields-row__column.fields-row__column-6.fields-group
-      = f.input :registrations_mode, collection: %w(open approved none), wrapper: :with_label, include_blank: false, label_method: ->(mode) { I18n.t("admin.settings.registrations_mode.modes.#{mode}") }
+      = f.input :registrations_mode, collection: %w(open approved none), wrapper: :with_label, include_blank: false, label_method: ->(mode) { I18n.t("admin.settings.registrations_mode.modes.#{mode}") }, warning_hint: I18n.t('admin.settings.registrations_mode.warning_hint')
 
     .fields-row__column.fields-row__column-6.fields-group
       = f.input :require_invite_text, as: :boolean, wrapper: :with_label, disabled: !approved_registrations?
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 85a0a9ff94511f..7db5e1bad12a8d 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -764,6 +764,7 @@ en:
         disabled: To no one
         users: To logged-in local users
       registrations:
+        moderation_recommandation: Please make sure you have an adequate and reactive moderation team before you open registrations to everyone!
         preamble: Control who can create an account on your server.
         title: Registrations
       registrations_mode:
@@ -771,6 +772,7 @@ en:
           approved: Approval required for sign up
           none: Nobody can sign up
           open: Anyone can sign up
+        warning_hint: We recommend using “Approval required for sign up” unless you are confident your moderation team can handle spam and malicious registrations in a timely fashion.
       security:
         authorized_fetch: Require authentication from federated servers
         authorized_fetch_hint: Requiring authentication from federated servers enables stricter enforcement of both user-level and server-level blocks. However, this comes at the cost of a performance penalty, reduces the reach of your replies, and may introduce compatibility issues with some federated services. In addition, this will not prevent dedicated actors from fetching your public posts and accounts.
diff --git a/config/settings.yml b/config/settings.yml
index 67297c26ceafcf..208c8e3760c2e5 100644
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -9,7 +9,7 @@ defaults: &defaults
   site_terms: ''
   site_contact_username: ''
   site_contact_email: ''
-  registrations_mode: 'open'
+  registrations_mode: 'none'
   profile_directory: true
   closed_registrations_message: ''
   timeline_preview: true
diff --git a/spec/models/setting_spec.rb b/spec/models/setting_spec.rb
index 5ed5c5d766c5ec..97e548e0996c39 100644
--- a/spec/models/setting_spec.rb
+++ b/spec/models/setting_spec.rb
@@ -142,22 +142,12 @@
     context 'when records includes nothing' do
       let(:records) { [] }
 
-      context 'when default_value is not a Hash' do
-        it 'includes Setting with value of default_value' do
-          setting = described_class.all_as_records[key]
-
-          expect(setting).to be_a described_class
-          expect(setting).to have_attributes(var: key)
-          expect(setting).to have_attributes(value: 'default_value')
-        end
-      end
-
-      context 'when default_value is a Hash' do
-        let(:default_value) { { 'foo' => 'fuga' } }
+      it 'includes Setting with value of default_value' do
+        setting = described_class.all_as_records[key]
 
-        it 'returns {}' do
-          expect(described_class.all_as_records).to eq({})
-        end
+        expect(setting).to be_a described_class
+        expect(setting).to have_attributes(var: key)
+        expect(setting).to have_attributes(value: default_value)
       end
     end
   end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index b4c20545f541a1..030bc81fb36642 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -31,6 +31,12 @@
   config.before :suite do
     Rails.application.load_seed
     Chewy.strategy(:bypass)
+
+    # NOTE: we switched registrations mode to closed by default, but the specs
+    # very heavily rely on having it enabled by default, as it relies on users
+    # being approved by default except in select cases where explicitly testing
+    # other registration modes
+    Setting.registrations_mode = 'open'
   end
 
   config.after :suite do