diff --git a/lib/js_of_ocaml/json.mli b/lib/js_of_ocaml/json.mli
index 45641c2d9f..1d0f38d413 100644
--- a/lib/js_of_ocaml/json.mli
+++ b/lib/js_of_ocaml/json.mli
@@ -28,8 +28,6 @@ val unsafe_input : Js.js_string Js.t -> 'a
 
 (**/**)
 
-val output_ : 'a -> string
-
 val set_use_native_stringify : bool -> unit
 (** Only affects js_of_ocaml. Whether to use native Javascript [stringify] to
     turn a value into JSON in {!val:output}. Otherwise, fall back to the slower