diff --git a/SWIG/Lib/ocaml/swig.ml b/SWIG/Lib/ocaml/swig.ml
index ff58fc575..60917c57e 100644
--- a/SWIG/Lib/ocaml/swig.ml
+++ b/SWIG/Lib/ocaml/swig.ml
@@ -31,7 +31,7 @@ exception NotObject of empty_enum c_obj_t
 exception NotEnumType of empty_enum c_obj_t
 exception LabelNotFromThisEnum of empty_enum c_obj_t
 
-let invoke obj = match obj with C_obj o -> o | _ -> raise (NotObject obj)
+let invoke obj = match obj with C_obj o -> o | _ -> raise (NotObject (Obj.magic obj))
 let _ = Callback.register "swig_runmethod" invoke
 let fnhelper fin f arg =
   let args = match arg with C_list l -> l | C_void -> [] | _ -> [ arg ] in
diff --git a/SWIG/Lib/ocaml/swig.mli b/SWIG/Lib/ocaml/swig.mli
index bc3673a7d..e7198b73b 100644
--- a/SWIG/Lib/ocaml/swig.mli
+++ b/SWIG/Lib/ocaml/swig.mli
@@ -20,6 +20,7 @@ type 'a c_obj_t =
   | C_enum of 'a
   | C_director_core of 'a c_obj_t * 'a c_obj_t option ref
 
+val invoke : 'a c_obj_t -> (string -> 'a c_obj_t -> 'a c_obj_t)
 val convert_c_obj : 'a c_obj_t -> 'b c_obj_t
 
 val get_int : 'a c_obj_t -> int