diff --git a/esp8266/main.c b/esp8266/main.c
index e3188dfe4077d9ca698ed8709a38ecdd2973655b..43b83759ecb34c48f293535a0566282b349ec6d2 100644
--- a/esp8266/main.c
+++ b/esp8266/main.c
@@ -122,7 +122,7 @@ 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);
diff --git a/minimal/main.c b/minimal/main.c
index 114fb96950a46875760ba7deb221cb1fcc52a241..e28cfe45eb2adad547a2c0ab5c68c8834fd17740 100644
--- a/minimal/main.c
+++ b/minimal/main.c
@@ -77,7 +77,7 @@ 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);
diff --git a/pic16bit/main.c b/pic16bit/main.c
index 7de790069ba82383bd4d37eb3e613b68d18a812e..343fe86d0599bc35c8ac9e7cb5e0c333a1c8e49c 100644
--- a/pic16bit/main.c
+++ b/pic16bit/main.c
@@ -106,7 +106,7 @@ 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);