diff --git a/lib/marginalia/railtie.rb b/lib/marginalia/railtie.rb
index 8bf0f6c..7bc70d6 100644
--- a/lib/marginalia/railtie.rb
+++ b/lib/marginalia/railtie.rb
@@ -40,7 +40,7 @@ def self.insert_into_active_job
 
     def self.insert_into_action_controller
       ActionController::Base.send(:include, ActionControllerInstrumentation)
-      if defined? ActionController::API
+      ActiveSupport.on_load :action_controller_api do
         ActionController::API.send(:include, ActionControllerInstrumentation)
       end
     end