diff --git a/actionpack/lib/action_dispatch/testing/assertion_response.rb b/actionpack/lib/action_dispatch/testing/assertion_response.rb
index 79af372cc19c0..4363fc868a361 100644
--- a/actionpack/lib/action_dispatch/testing/assertion_response.rb
+++ b/actionpack/lib/action_dispatch/testing/assertion_response.rb
@@ -36,7 +36,7 @@ def code_and_name
 
     private
       def code_from_name(name)
-        GENERIC_RESPONSE_CODES[name] || Rack::Utils::SYMBOL_TO_STATUS_CODE[name]
+        GENERIC_RESPONSE_CODES[name] || Rack::Utils.status_code(name)
       end
 
       def name_from_code(code)