diff --git a/boards/px4/fmu-v6c/init/rc.board_sensors b/boards/px4/fmu-v6c/init/rc.board_sensors
index 34afb338dcf..1382aa87c51 100644
--- a/boards/px4/fmu-v6c/init/rc.board_sensors
+++ b/boards/px4/fmu-v6c/init/rc.board_sensors
@@ -25,7 +25,11 @@ fi
 ms5611 -X -b 4 -a 0x77 start
 
 # Internal compass on IMU I2C4 (The same bus is also exposed externally, and therefore marked as external)
-ist8310 -X -b 4 -a 0xc  start
+# Standard FMUv6C uses IST8310; the variant board falls back to RM3100.
+if ! ist8310 -X -b 4 -a 0xc -q start
+then
+	rm3100 -X -b 4 -R 8 start
+fi
 
 # External compass on GPS/I2C1 (the 3rd external bus): standard Holybro Pixhawk 4 or CUAV V5 GPS/compass puck (with lights, safety button, and buzzer)
 ist8310 -X -b 1 -R 10 start
diff --git a/boards/px4/fmu-v6c/src/i2c.cpp b/boards/px4/fmu-v6c/src/i2c.cpp
index ab0a2bbe55d..64715f1ee7b 100644
--- a/boards/px4/fmu-v6c/src/i2c.cpp
+++ b/boards/px4/fmu-v6c/src/i2c.cpp
@@ -71,6 +71,17 @@ bool px4_i2c_device_external(const uint32_t device_id)
 		if (device_id_mag.devid == device_id) {
 			return false;
 		}
+
+		// device_id: RM3100 on I2C4 address 0x20
+		device::Device::DeviceId device_id_rm3100{};
+		device_id_rm3100.devid_s.bus_type = device::Device::DeviceBusType_I2C;
+		device_id_rm3100.devid_s.bus = 4;
+		device_id_rm3100.devid_s.address = 0x20;
+		device_id_rm3100.devid_s.devtype = DRV_MAG_DEVTYPE_RM3100;
+
+		if (device_id_rm3100.devid == device_id) {
+			return false;
+		}
 	}
 
 	device::Device::DeviceId dev_id{};