diff --git a/actionmailer/Rakefile b/actionmailer/Rakefile
index 96c84b986e..140661ecb0 100644
--- a/actionmailer/Rakefile
+++ b/actionmailer/Rakefile
@@ -24,7 +24,7 @@ Rake::TestTask.new { |t|
   t.libs << "test"
   t.pattern = 'test/*_test.rb'
   t.verbose = true
-  t.warning = false
+  t.warning = true
 }
 
 task :isolated_test do