diff --git a/config/discourse_defaults.conf b/config/discourse_defaults.conf
index eeb7412fb7..f0d34270d0 100644
--- a/config/discourse_defaults.conf
+++ b/config/discourse_defaults.conf
@@ -339,3 +339,9 @@ cluster_name =
 
 # The YAML file used to configure multisite clusters
 multisite_config_path = config/multisite.yml
+
+# If false, only short (regular) polling will be attempted
+enable_long_polling =
+
+# Length of time to hold open a long polling connection in milliseconds
+long_polling_interval =
diff --git a/config/initializers/004-message_bus.rb b/config/initializers/004-message_bus.rb
index fcc62b3f4e..f560ad2a32 100644
--- a/config/initializers/004-message_bus.rb
+++ b/config/initializers/004-message_bus.rb
@@ -119,8 +119,16 @@ else
 end
 MessageBus.reliable_pub_sub.max_backlog_size = GlobalSetting.message_bus_max_backlog_size
 
-MessageBus.long_polling_enabled = SiteSetting.enable_long_polling
-MessageBus.long_polling_interval = SiteSetting.long_polling_interval
+if SiteSetting.table_exists? && SiteSetting.where(name: ['enable_long_polling', 'long_polling_interval']).exists?
+  Discourse.deprecate("enable_long_polling/long_polling_interval have switched from site settings to global settings. Remove the override from the Site Settings UI, and use a config file or environment variables to set the global settings.", drop_from: '2.9.0')
+
+  MessageBus.long_polling_enabled = SiteSetting.enable_long_polling
+  MessageBus.long_polling_interval = SiteSetting.long_polling_interval
+else
+  MessageBus.long_polling_enabled = GlobalSetting.enable_long_polling.nil? ? true : GlobalSetting.enable_long_polling
+  MessageBus.long_polling_interval = GlobalSetting.long_polling_interval || 25000
+end
+
 MessageBus.cache_assets = !Rails.env.development?
 MessageBus.enable_diagnostics