diff --git a/actionpack/test/template/asset_tag_helper_test.rb b/actionpack/test/template/asset_tag_helper_test.rb
index ac21bc2a33..a836962678 100644
--- a/actionpack/test/template/asset_tag_helper_test.rb
+++ b/actionpack/test/template/asset_tag_helper_test.rb
@@ -46,7 +46,7 @@ class AssetTagHelperTest < Test::Unit::TestCase
   def teardown
     ActionController::Base.perform_caching = false
     ActionController::Base.asset_host = nil
-    ENV["RAILS_ASSET_ID"] = nil
+    ENV.delete('RAILS_ASSET_ID')
   end
 
   AutoDiscoveryToTag = {