Dialyzer Unknown type for struct

Background

I have a custom struct and I want to define a type for it so I can run Dialyzer checks. However Dialyzer is complaining that I have an unknown type.

Code

I have a struct that defines an Event and I have defined the following type:

defmodule MyApp.Event do

  @enforce_keys [:event_id, :type, :version]
  defstruct event_id: nil,
            type: "event",
            version: nil

  @type t() :: %__MODULE__{
          event_id: non_neg_integer,
          type: String.t(),
          version: non_neg_integer
        }

  @spec new(map) :: __MODULE__.t()
  def new(map),
    do: %__MODULE__{
      event_id: Map.get(map, "event_id"),
      type: Map.get(map, "type"),
      version: Map.get(map, "v")
    }
end

Problem

However when I run mix dialyzer I get the following error:

:0: Unknown type ‘Elixir.Event’:t/0

What am I missing?