diff --git a/boards/px4/fmu-v6x/default.px4board b/boards/px4/fmu-v6x/default.px4board
index 60bb22729c..d6b0cc1313 100644
--- a/boards/px4/fmu-v6x/default.px4board
+++ b/boards/px4/fmu-v6x/default.px4board
@@ -6,6 +6,7 @@ CONFIG_BOARD_SERIAL_GPS2="/dev/ttyS7"
 CONFIG_BOARD_SERIAL_TEL1="/dev/ttyS6"
 CONFIG_BOARD_SERIAL_TEL2="/dev/ttyS4"
 CONFIG_BOARD_SERIAL_TEL3="/dev/ttyS1"
+CONFIG_BOARD_SERIAL_EXT2="/dev/ttyS3"
 CONFIG_DRIVERS_ADC_BOARD_ADC=y
 CONFIG_DRIVERS_BAROMETER_BMP388=y
 CONFIG_DRIVERS_BAROMETER_INVENSENSE_ICP201XX=y