diff --git a/app/javascript/packs/admin.jsx b/app/javascript/packs/admin.jsx
index d3bfc4ea90f..817a5d46bc9 100644
--- a/app/javascript/packs/admin.jsx
+++ b/app/javascript/packs/admin.jsx
@@ -145,6 +145,10 @@ Rails.delegate(document, '#form_admin_settings_enable_bootstrap_timeline_account
 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 168f1097570..4ece27bf4e7 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 a7a83391d46..efd603740a7 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -767,6 +767,7 @@ 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:
@@ -774,6 +775,7 @@ 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 67297c26cea..208c8e3760c 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/spec_helper.rb b/spec/spec_helper.rb
index dc60976d05f..8a01792a199 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -23,6 +23,12 @@ RSpec.configure do |config|
   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
diff --git a/spec/support/streaming_server_manager.rb b/spec/support/streaming_server_manager.rb
index 39657586f24..33819182990 100644
--- a/spec/support/streaming_server_manager.rb
+++ b/spec/support/streaming_server_manager.rb
@@ -102,6 +102,13 @@ RSpec.configure do |config|
     self.use_transactional_tests = false
 
     DatabaseCleaner.cleaning do
+      # 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
+      # Also needs to be set per-example here because of the database cleaner.
+      Setting.registrations_mode = 'open'
+
       example.run
     end