diff --git a/extmod/fsusermount.c b/extmod/fsusermount.c
index 4ce731d171..d86e57b4b8 100644
--- a/extmod/fsusermount.c
+++ b/extmod/fsusermount.c
@@ -150,7 +150,7 @@ mkfs_error:
     }
 }
 
-STATIC mp_obj_t fatfs_mount(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+STATIC mp_obj_t fatfs_mount(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     fatfs_mount_mkfs(n_args, pos_args, kw_args, false);
     return mp_const_none;
 }
@@ -193,7 +193,7 @@ STATIC mp_obj_t fatfs_umount(mp_obj_t bdev_or_path_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(fsuser_umount_obj, fatfs_umount);
 
-STATIC mp_obj_t fatfs_mkfs(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+STATIC mp_obj_t fatfs_mkfs(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     fatfs_mount_mkfs(n_args, pos_args, kw_args, true);
     return mp_const_none;
 }
diff --git a/extmod/vfs_fat.c b/extmod/vfs_fat.c
index f7c31408ff..607a736a78 100644
--- a/extmod/vfs_fat.c
+++ b/extmod/vfs_fat.c
@@ -41,7 +41,7 @@ STATIC mp_obj_t fat_vfs_make_new(const mp_obj_type_t *type, size_t n_args, size_
     mp_arg_check_num(n_args, n_kw, 2, 2, false);
     mp_obj_fat_vfs_t *vfs = fatfs_mount_mkfs(n_args, args, (mp_map_t*)&mp_const_empty_map, false);
     vfs->base.type = type;
-    return vfs;
+    return MP_OBJ_FROM_PTR(vfs);
 }
 
 STATIC mp_obj_t fat_vfs_mkfs(mp_obj_t bdev_in) {
@@ -52,7 +52,7 @@ STATIC mp_obj_t fat_vfs_mkfs(mp_obj_t bdev_in) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(fat_vfs_mkfs_fun_obj, fat_vfs_mkfs);
 STATIC MP_DEFINE_CONST_STATICMETHOD_OBJ(fat_vfs_mkfs_obj, MP_ROM_PTR(&fat_vfs_mkfs_fun_obj));
 
-mp_obj_t fat_vfs_open(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+STATIC mp_obj_t fat_vfs_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     // Skip self
     return fatfs_builtin_open(n_args - 1, args + 1, kwargs);
 }