How can I use timestamps in Absinthe? (Phoenix 1.3)

I have a problem with phoenix 1.3 + absinthe.

I try this code:

schema "urls" do
  field :path, :string

  timestamps()
 end

object :url do
  field :id, :id
  field :path, :string
  field :inserted_at, :datetime
end

It work with id and path but it fails with inserted_at with:

Inserted_at :datetime is not defined in your schema.          

Types must exist if referenced.   


lib/absinthe/schema.ex:230: Absinthe.Schema.__after_compile__/2     
(stdlib) erl_eval.erl:670: :erl_eval.do_apply/6                     
(elixir) lib/kernel/parallel_compiler.ex:121: anonymous fn/4 in Kernel.ParallelCompiler.spawn_compilers/1