diff --git a/stmhal/sdcard.c b/stmhal/sdcard.c
index b1d67f62ab..f4ad985048 100644
--- a/stmhal/sdcard.c
+++ b/stmhal/sdcard.c
@@ -447,6 +447,7 @@ void sdcard_init_vfs(fs_user_mount_t *vfs) {
     vfs->base.type = &mp_fat_vfs_type;
     vfs->flags |= FSUSER_NATIVE | FSUSER_HAVE_IOCTL;
     vfs->fatfs.drv = vfs;
+    vfs->fatfs.part = 0; // autodetect partition
     vfs->readblocks[0] = (mp_obj_t)&pyb_sdcard_readblocks_obj;
     vfs->readblocks[1] = (mp_obj_t)&pyb_sdcard_obj;
     vfs->readblocks[2] = (mp_obj_t)sdcard_read_blocks; // native version
diff --git a/stmhal/storage.c b/stmhal/storage.c
index 0a5b507394..ed8b4e87a2 100644
--- a/stmhal/storage.c
+++ b/stmhal/storage.c
@@ -507,6 +507,7 @@ void pyb_flash_init_vfs(fs_user_mount_t *vfs) {
     vfs->base.type = &mp_fat_vfs_type;
     vfs->flags |= FSUSER_NATIVE | FSUSER_HAVE_IOCTL;
     vfs->fatfs.drv = vfs;
+    vfs->fatfs.part = 1; // flash filesystem lives on first partition
     vfs->readblocks[0] = (mp_obj_t)&pyb_flash_readblocks_obj;
     vfs->readblocks[1] = (mp_obj_t)&pyb_flash_obj;
     vfs->readblocks[2] = (mp_obj_t)storage_read_blocks; // native version