diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index caa1b0deb6ff2609b76265c09e9cbd35c30cb7db..199c7038c47ebcca35943954321f20899dcb30b3 100644
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -44,6 +44,7 @@ static efi_status_t fdt_init_moc_mode(void *fdt, int node)
 	if (!efi_pbha)
 		goto out;
 
+	size = sizeof(hbm_mode);
 	efi_status = get_efi_var(L"MemoryOnChipMode", &oem_config_guid, NULL, &size,
 				 &hbm_mode);
 	if (efi_status != EFI_SUCCESS)