diff --git a/libraries/AP_InertialSensor/AP_InertialSensor.cpp b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
index 6acf2d5e6a..5040188573 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
@@ -691,6 +691,7 @@ AP_InertialSensor::detect_backends(void)
     } else if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_PIXHAWK) {
         if (!_add_backend(AP_InertialSensor_MPU6000::probe(*this, hal.spi->get_device(HAL_INS_MPU60x0_NAME), ROTATION_ROLL_180))) {
             // handle pixfalcon with mpu9250 instead of mpu6000
+            _fast_sampling_mask.set_default(1);
             _add_backend(AP_InertialSensor_MPU9250::probe(*this, hal.spi->get_device(HAL_INS_MPU9250_NAME), ROTATION_ROLL_180));
         }
         _add_backend(AP_InertialSensor_LSM9DS0::probe(*this,
@@ -700,6 +701,7 @@ AP_InertialSensor::detect_backends(void)
 
     } else if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_PIXHAWK2) {
         // older Pixhawk2 boards have the MPU6000 instead of MPU9250
+        _fast_sampling_mask.set_default(1);
         if (!_add_backend(AP_InertialSensor_MPU9250::probe(*this, hal.spi->get_device(HAL_INS_MPU9250_EXT_NAME), ROTATION_PITCH_180))) {
             _add_backend(AP_InertialSensor_MPU6000::probe(*this, hal.spi->get_device(HAL_INS_MPU60x0_EXT_NAME), ROTATION_PITCH_180));
         }
@@ -712,15 +714,18 @@ AP_InertialSensor::detect_backends(void)
         }
 
     } else if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_PIXRACER) {
+        _fast_sampling_mask.set_default(3);
         _add_backend(AP_InertialSensor_MPU6000::probe(*this, hal.spi->get_device(HAL_INS_ICM20608_NAME), ROTATION_ROLL_180_YAW_90));
         _add_backend(AP_InertialSensor_MPU9250::probe(*this, hal.spi->get_device(HAL_INS_MPU9250_NAME), ROTATION_ROLL_180_YAW_90));
 
     } else if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_PHMINI) {
         // PHMINI uses ICM20608 on the ACCEL_MAG device and a MPU9250 on the old MPU6000 CS line
+        _fast_sampling_mask.set_default(3);
         _add_backend(AP_InertialSensor_MPU6000::probe(*this, hal.spi->get_device(HAL_INS_ICM20608_AM_NAME), ROTATION_ROLL_180));
         _add_backend(AP_InertialSensor_MPU9250::probe(*this, hal.spi->get_device(HAL_INS_MPU9250_NAME), ROTATION_ROLL_180));
 
     } else if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_PH2SLIM) {
+        _fast_sampling_mask.set_default(1);
         _add_backend(AP_InertialSensor_MPU9250::probe(*this, hal.spi->get_device(HAL_INS_MPU9250_NAME), ROTATION_YAW_270));
     }
     // also add any PX4 backends (eg. canbus sensors)