diff --git a/boards/px4/fmu-v3/init/rc.board_sensors b/boards/px4/fmu-v3/init/rc.board_sensors
index 33e5698d76..49af4d46ee 100644
--- a/boards/px4/fmu-v3/init/rc.board_sensors
+++ b/boards/px4/fmu-v3/init/rc.board_sensors
@@ -33,6 +33,12 @@ then
 		if mpu9250 -s -b 4 -R 10 start
 		then
 			set BOARD_FMUV3 21
+		else
+
+			# some boards have an internal hmc5883 or ist8310, make sure they
+			# are not detected as external
+			hmc5883 start -X -b 2 -i
+			ist8310 start -X -b 2 -i
 		fi
 	fi
 fi
diff --git a/src/drivers/magnetometer/hmc5883/HMC5883.cpp b/src/drivers/magnetometer/hmc5883/HMC5883.cpp
index fdf0a9353e..1fd7074f4b 100644
--- a/src/drivers/magnetometer/hmc5883/HMC5883.cpp
+++ b/src/drivers/magnetometer/hmc5883/HMC5883.cpp
@@ -48,7 +48,7 @@ HMC5883::HMC5883(device::Device *interface, const I2CSPIDriverConfig &config) :
 	_temperature_counter(0),
 	_temperature_error_count(0)
 {
-	_px4_mag.set_external(_interface->external());
+	_px4_mag.set_external(config.custom2 != 1 && _interface->external());
 }
 
 HMC5883::~HMC5883()
diff --git a/src/drivers/magnetometer/hmc5883/hmc5883_main.cpp b/src/drivers/magnetometer/hmc5883/hmc5883_main.cpp
index a8fa83f4f6..d2bf390ef4 100644
--- a/src/drivers/magnetometer/hmc5883/hmc5883_main.cpp
+++ b/src/drivers/magnetometer/hmc5883/hmc5883_main.cpp
@@ -96,6 +96,7 @@ void HMC5883::print_usage()
 	PRINT_MODULE_USAGE_PARAMS_I2C_SPI_DRIVER(true, true);
 	PRINT_MODULE_USAGE_PARAM_INT('R', 0, 0, 35, "Rotation", true);
 	PRINT_MODULE_USAGE_PARAM_FLAG('T', "Enable temperature compensation", true);
+	PRINT_MODULE_USAGE_PARAM_FLAG('i', "Force as internal", true);
 	PRINT_MODULE_USAGE_DEFAULT_COMMANDS();
 }
 
@@ -107,7 +108,7 @@ extern "C" int hmc5883_main(int argc, char *argv[])
 	cli.default_i2c_frequency = 400000;
 	cli.default_spi_frequency = 11 * 1000 * 1000;
 
-	while ((ch = cli.getOpt(argc, argv, "R:T")) != EOF) {
+	while ((ch = cli.getOpt(argc, argv, "R:Ti")) != EOF) {
 		switch (ch) {
 		case 'R':
 			cli.rotation = (enum Rotation)atoi(cli.optArg());
@@ -116,6 +117,10 @@ extern "C" int hmc5883_main(int argc, char *argv[])
 		case 'T':
 			cli.custom1 = 1;
 			break;
+
+		case 'i':
+			cli.custom2 = 1;
+			break;
 		}
 	}
 
diff --git a/src/drivers/magnetometer/isentek/ist8310/IST8310.cpp b/src/drivers/magnetometer/isentek/ist8310/IST8310.cpp
index cc98c5df60..d4d277a115 100644
--- a/src/drivers/magnetometer/isentek/ist8310/IST8310.cpp
+++ b/src/drivers/magnetometer/isentek/ist8310/IST8310.cpp
@@ -45,7 +45,7 @@ IST8310::IST8310(const I2CSPIDriverConfig &config) :
 	I2CSPIDriver(config),
 	_px4_mag(get_device_id(), config.rotation)
 {
-	_px4_mag.set_external(external());
+	_px4_mag.set_external(config.custom2 != 1 && external());
 }
 
 IST8310::~IST8310()
diff --git a/src/drivers/magnetometer/isentek/ist8310/ist8310_main.cpp b/src/drivers/magnetometer/isentek/ist8310/ist8310_main.cpp
index eee1a01c1d..3731be2f03 100644
--- a/src/drivers/magnetometer/isentek/ist8310/ist8310_main.cpp
+++ b/src/drivers/magnetometer/isentek/ist8310/ist8310_main.cpp
@@ -44,6 +44,7 @@ void IST8310::print_usage()
 	PRINT_MODULE_USAGE_PARAMS_I2C_SPI_DRIVER(true, false);
 	PRINT_MODULE_USAGE_PARAMS_I2C_ADDRESS(0x0E);
 	PRINT_MODULE_USAGE_PARAM_INT('R', 0, 0, 35, "Rotation", true);
+	PRINT_MODULE_USAGE_PARAM_FLAG('i', "Force as internal", true);
 	PRINT_MODULE_USAGE_DEFAULT_COMMANDS();
 }
 
@@ -55,11 +56,15 @@ extern "C" int ist8310_main(int argc, char *argv[])
 	cli.i2c_address = I2C_ADDRESS_DEFAULT;
 	cli.default_i2c_frequency = I2C_SPEED;
 
-	while ((ch = cli.getOpt(argc, argv, "R:")) != EOF) {
+	while ((ch = cli.getOpt(argc, argv, "R:i")) != EOF) {
 		switch (ch) {
 		case 'R':
 			cli.rotation = (enum Rotation)atoi(cli.optArg());
 			break;
+
+		case 'i':
+			cli.custom2 = 1;
+			break;
 		}
 	}