diff --git a/actionpack/lib/action_view/helpers/form_helper.rb b/actionpack/lib/action_view/helpers/form_helper.rb
index 6d70c63de98f6fe20729119535221620201e64e7..79a9d997dd3b64a52f7b4c5c1f6363e83b35f48f 100644
--- a/actionpack/lib/action_view/helpers/form_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_helper.rb
@@ -306,11 +306,11 @@ def form_for(record, record_object = nil, options = nil, &proc)
           object = record_object
         when Array
           object = record.last
-          object_name = options[:as] || ActiveModel::Naming.singular(object)
+          object_name = options[:as] || ActiveModel::Naming.param_key(object)
           apply_form_for_options!(record, options)
         else
           object = record
-          object_name = options[:as] || ActiveModel::Naming.singular(object)
+          object_name = options[:as] || ActiveModel::Naming.param_key(object)
           apply_form_for_options!([object], options)
         end