diff --git a/python/port/port.c b/python/port/port.c
index 10ec4847c..f11a23416 100644
--- a/python/port/port.c
+++ b/python/port/port.c
@@ -47,7 +47,7 @@ mp_import_stat_t mp_import_stat(const char *path) {
     return MP_IMPORT_STAT_NO_EXIST;
 }
 
-mp_obj_t mp_builtin_open(uint n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);