diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index 16782a894ec89244d1b6b886e4ddd597e2641296..4aee4899121f359e81e191ee4ddbe9fd3babaeb8 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -381,8 +381,6 @@ def to_ary
     end
 
     def rack_response(status, header)
-      header[SET_COOKIE] = header[SET_COOKIE].join("\n") if header[SET_COOKIE].respond_to?(:join)
-
       if NO_CONTENT_CODES.include?(@status)
         header.delete CONTENT_TYPE
         header.delete 'Content-Length'