diff --git a/lib/tabular_form_builder.rb b/lib/tabular_form_builder.rb
index bfa6e1790..7dbf6fc00 100644
--- a/lib/tabular_form_builder.rb
+++ b/lib/tabular_form_builder.rb
@@ -20,7 +20,8 @@ require 'action_view/helpers/form_helper'
 class TabularFormBuilder < ActionView::Helpers::FormBuilder
   include Redmine::I18n
 
-  (field_helpers - %w(radio_button hidden_field fields_for) + %w(date_select)).each do |selector|
+  (field_helpers.map(&:to_s) - %w(radio_button hidden_field fields_for) +
+        %w(date_select)).each do |selector|
     src = <<-END_SRC
     def #{selector}(field, options = {})
       label_for_field(field, options) + super