diff --git a/include/libpldm/firmware_update.h b/include/libpldm/firmware_update.h
index 73dabe3..272a483 100644
--- a/include/libpldm/firmware_update.h
+++ b/include/libpldm/firmware_update.h
@@ -568,6 +568,7 @@
 	uint16_t downstream_device_index;
 	uint8_t downstream_descriptor_count;
 };
+#define PLDM_DOWNSTREAM_DEVICE_BYTES 3
 
 /** @struct pldm_query_downstream_firmware_param_req
  *