diff --git a/actionpack/lib/action_controller/caching.rb b/actionpack/lib/action_controller/caching.rb
index 92eb8770df741b2f9a8316e5a839a17d2570b2ad..5ea5ab94ec5c29b39f9d010cec051a5eb9920d25 100644
--- a/actionpack/lib/action_controller/caching.rb
+++ b/actionpack/lib/action_controller/caching.rb
@@ -443,7 +443,7 @@ def cache_sweeper(*sweepers)
       end
     end
     
-    if defined?("ActiveRecord")
+    if defined?(ActiveRecord::Observer)
       class Sweeper < ActiveRecord::Observer
         attr_accessor :controller