diff --git a/actionpack/lib/action_view/helpers/translation_helper.rb b/actionpack/lib/action_view/helpers/translation_helper.rb
index a42e5542f2..7d954b3a2f 100644
--- a/actionpack/lib/action_view/helpers/translation_helper.rb
+++ b/actionpack/lib/action_view/helpers/translation_helper.rb
@@ -29,7 +29,7 @@ module ActionView
       private
 
         def scope_key_by_partial(key)
-          if key.to_s.first == "."
+          if (key.respond_to?(:join) ? key.join : key.to_s).first == "."
             if @_virtual_path
               @_virtual_path.gsub(%r{/_?}, ".") + key.to_s
             else