diff --git a/config/config.exs b/config/config.exs
index 0daae2301..435d81425 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -62,7 +62,15 @@ config :logger,
 config :phoenix, :json_library, Jason
 
 config :phoenix, :template_engines, md: PhoenixMarkdown.Engine
-config :phoenix_template, :format_encoders, svg: Phoenix.HTML.Engine, xml: Phoenix.HTML.Engine
+
+config :phoenix_template, :format_encoders,
+  cast: Jason,
+  svg: Phoenix.HTML.Engine,
+  xml: Phoenix.HTML.Engine
+
+config :mime, :types, %{
+  "application/x-asciicast" => ["cast"]
+}
 
 config :sentry,
   dsn: "https://public:secret@sentry.io/1",
diff --git a/lib/asciinema_web/controllers/fallback_controller.ex b/lib/asciinema_web/controllers/fallback_controller.ex
index 9c7f103e1..e2cdac8cf 100644
--- a/lib/asciinema_web/controllers/fallback_controller.ex
+++ b/lib/asciinema_web/controllers/fallback_controller.ex
@@ -12,6 +12,7 @@ defmodule AsciinemaWeb.FallbackController do
     |> put_view(
       html: AsciinemaWeb.ErrorHTML,
       json: AsciinemaWeb.ErrorJSON,
+      cast: AsciinemaWeb.ErrorJSON,
       txt: AsciinemaWeb.ErrorTEXT,
       svg: AsciinemaWeb.ErrorTEXT,
       xml: AsciinemaWeb.ErrorTEXT