diff --git a/ports/stm32/main.c b/ports/stm32/main.c
index e2b3f3c36..8cb6ed1e3 100644
--- a/ports/stm32/main.c
+++ b/ports/stm32/main.c
@@ -222,8 +222,8 @@ MP_NOINLINE STATIC bool init_flash_fs(uint reset_mode) {
 
     if (len != -1) {
         // Detected a littlefs filesystem so create correct block device for it
-        mp_obj_t args[] = { MP_OBJ_NEW_SMALL_INT(0), MP_OBJ_NEW_SMALL_INT(len) };
-        bdev = pyb_flash_type.make_new(&pyb_flash_type, 2, 0, args);
+        mp_obj_t args[] = { MP_OBJ_NEW_QSTR(MP_QSTR_len), MP_OBJ_NEW_SMALL_INT(len) };
+        bdev = pyb_flash_type.make_new(&pyb_flash_type, 0, 1, args);
     }
 
     #endif