diff --git a/sdkconfig.defaults b/sdkconfig.defaults
index 6c55a68..6792886 100644
--- a/sdkconfig.defaults
+++ b/sdkconfig.defaults
@@ -7,3 +7,6 @@ CONFIG_TINYUSB_HID_COUNT=1
 CONFIG_PARTITION_TABLE_CUSTOM=y
 CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="u2f_partitions.csv"
 CONFIG_PARTITION_TABLE_FILENAME="u2f_partitions.csv"
+
+# automatic flash size update when esptool is used, used for detecting board
+CONFIG_ESPTOOLPY_HEADER_FLASHSIZE_UPDATE=y