diff --git a/tools/ocaml/libs/xb/xenbus_stubs.c b/tools/ocaml/libs/xb/xenbus_stubs.c
index 3065181a55..97116b0782 100644
--- a/tools/ocaml/libs/xb/xenbus_stubs.c
+++ b/tools/ocaml/libs/xb/xenbus_stubs.c
@@ -30,10 +30,9 @@
 #include <xenctrl.h>
 #include <xen/io/xs_wire.h>
 
-CAMLprim value stub_header_size(void)
+CAMLprim value stub_header_size(value unit)
 {
-	CAMLparam0();
-	CAMLreturn(Val_int(sizeof(struct xsd_sockmsg)));
+	return Val_int(sizeof(struct xsd_sockmsg));
 }
 
 CAMLprim value stub_header_of_string(value s)
diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c b/tools/ocaml/libs/xc/xenctrl_stubs.c
index 2fba9c5e94..7288184459 100644
--- a/tools/ocaml/libs/xc/xenctrl_stubs.c
+++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
@@ -86,9 +86,9 @@ static void Noreturn failwith_xc(xc_interface *xch)
 	caml_raise_with_string(*caml_named_value("xc.error"), error_str);
 }
 
-CAMLprim value stub_xc_interface_open(void)
+CAMLprim value stub_xc_interface_open(value unit)
 {
-	CAMLparam0();
+	CAMLparam1(unit);
 	CAMLlocal1(result);
 	xc_interface *xch;