diff --git a/Lib/ocaml/preamble.swg b/Lib/ocaml/preamble.swg
new file mode 100644
index 000000000..508371c51
--- /dev/null
+++ b/Lib/ocaml/preamble.swg
@@ -0,0 +1,21 @@
+%insert(mli) %{
+type c_obj = c_enum_tag c_obj_t
+
+exception BadArgs of string
+exception BadMethodName of c_obj * string * string
+exception NotObject of c_obj
+exception NotEnumType of c_obj
+exception LabelNotFromThisEnum of c_obj
+
+val invoke : c_obj -> (string -> c_obj -> c_obj)
+%}
+
+%insert(ml) %{
+type c_obj = c_enum_tag c_obj_t
+
+exception BadArgs of string
+exception BadMethodName of c_obj * string * string
+exception NotObject of c_obj
+exception NotEnumType of c_obj
+exception LabelNotFromThisEnum of c_obj
+%}
\ No newline at end of file