diff --git a/ROMFS/px4fmu_common/init.d/rcS b/ROMFS/px4fmu_common/init.d/rcS
index 44b85c35bc..a1105ca2a4 100644
--- a/ROMFS/px4fmu_common/init.d/rcS
+++ b/ROMFS/px4fmu_common/init.d/rcS
@@ -542,8 +542,12 @@ then
 			# Exit from nsh to free port for mavlink
 			set EXIT_ON_END yes
 		else
-			# Start MAVLink on default port: ttyS1
 			set MAVLINK_F "-r 1200"
+			# Avoid using ttyS1 for MAVLink on FMUv4
+			if ver hwcmp PX4FMU_V4
+			then
+				set MAVLINK_F "-r 1200 -d /dev/ttyS2"
+			fi
 		fi
 	fi