diff --git a/doc/README.android-fastboot b/doc/README.android-fastboot
index f1d128c..4045727 100644
--- a/doc/README.android-fastboot
+++ b/doc/README.android-fastboot
@@ -38,6 +38,10 @@
 CONFIG_G_DNL_PRODUCT_NUM
 CONFIG_G_DNL_MANUFACTURER
 
+NOTE: The CONFIG_G_DNL_VENDOR_NUM must be one of the numbers supported by
+the fastboot client. The list of vendor IDs supported can be found in the
+fastboot client source code (fastboot.c) mentioned above.
+
 The fastboot function is enabled by defining CONFIG_CMD_FASTBOOT and
 CONFIG_ANDROID_BOOT_IMAGE.