diff --git a/boards/px4/fmu-v5x/src/board_config.h b/boards/px4/fmu-v5x/src/board_config.h
index 2fe1654b65..aaa7c21df8 100644
--- a/boards/px4/fmu-v5x/src/board_config.h
+++ b/boards/px4/fmu-v5x/src/board_config.h
@@ -287,9 +287,12 @@
 #define GPIO_PPM_IN             /* PI5 T8C1 */ GPIO_TIM8_CH1IN_2
 
 /* RC Serial port */
-
 #define RC_SERIAL_PORT                     "/dev/ttyS5"
+/* Some RC protocols are bi-directional, therefore we need a half-duplex UART */
 #define RC_SERIAL_SINGLEWIRE
+/* The STM32 UART by default wires half-duplex mode to the TX pin, but our
+ * signal in routed to the RX pin, so we need to swap the pins */
+#define RC_SERIAL_SWAP_RXTX
 
 /* Input Capture Channels. */
 #define INPUT_CAP1_TIMER                  5
diff --git a/boards/px4/fmu-v6x/src/board_config.h b/boards/px4/fmu-v6x/src/board_config.h
index 7c98f94902..6590699a39 100644
--- a/boards/px4/fmu-v6x/src/board_config.h
+++ b/boards/px4/fmu-v6x/src/board_config.h
@@ -324,9 +324,12 @@
 #define GPIO_PPM_IN             /* PI5 T8C1 */ GPIO_TIM8_CH1IN_2
 
 /* RC Serial port */
-
 #define RC_SERIAL_PORT                     "/dev/ttyS5"
+/* Some RC protocols are bi-directional, therefore we need a half-duplex UART */
 #define RC_SERIAL_SINGLEWIRE
+/* The STM32 UART by default wires half-duplex mode to the TX pin, but our
+ * signal in routed to the RX pin, so we need to swap the pins */
+#define RC_SERIAL_SWAP_RXTX
 
 /* Input Capture Channels. */
 #define INPUT_CAP1_TIMER                  1