diff --git a/app/javascript/packs/admin.jsx b/app/javascript/packs/admin.jsx
index d3bfc4ea90fbd..817a5d46bc9a3 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 cae7a3394bab5..4ece27bf4e708 100644
--- a/app/views/admin/settings/registrations/show.html.haml
+++ b/app/views/admin/settings/registrations/show.html.haml
@@ -14,7 +14,7 @@
 
   .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 46b4d4a658612..330779134b132 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -775,6 +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.