diff --git a/activesupport/lib/active_support/descendants_tracker.rb b/activesupport/lib/active_support/descendants_tracker.rb
index 0c761d4f117..4fe496cd227 100644
--- a/activesupport/lib/active_support/descendants_tracker.rb
+++ b/activesupport/lib/active_support/descendants_tracker.rb
@@ -94,7 +94,7 @@ module ActiveSupport
         end
       else
         def descendants
-          children.concat(children.flat_map(&:descendants))
+          subclasses.concat(subclasses.flat_map(&:descendants))
         end
       end