diff --git a/libraries/AP_Compass/AP_Compass.h b/libraries/AP_Compass/AP_Compass.h
index be91d60962..b8d5aeead5 100644
--- a/libraries/AP_Compass/AP_Compass.h
+++ b/libraries/AP_Compass/AP_Compass.h
@@ -51,8 +51,12 @@
 #ifndef HAL_COMPASS_MAX_SENSORS
 #define HAL_COMPASS_MAX_SENSORS 3
 #endif
+#if HAL_COMPASS_MAX_SENSORS > 1
 #define COMPASS_MAX_UNREG_DEV 5
 #else
+#define COMPASS_MAX_UNREG_DEV 0
+#endif
+#else
 #ifndef HAL_COMPASS_MAX_SENSORS
 #define HAL_COMPASS_MAX_SENSORS 1
 #endif
diff --git a/libraries/AP_Compass/AP_Compass_Calibration.cpp b/libraries/AP_Compass/AP_Compass_Calibration.cpp
index b64cc80bdb..2f004b9929 100644
--- a/libraries/AP_Compass/AP_Compass_Calibration.cpp
+++ b/libraries/AP_Compass/AP_Compass_Calibration.cpp
@@ -53,10 +53,13 @@ bool Compass::_start_calibration(uint8_t i, bool retry, float delay)
         return false;
     }
     Priority prio = Priority(i);
+
+#if COMPASS_MAX_INSTANCES > 1
     if (_priority_did_list[prio] != _priority_did_stored_list[prio]) {
         gcs().send_text(MAV_SEVERITY_ERROR, "Compass cal requires reboot after priority change");
         return false;
     }
+#endif
     
     if (_calibrator[prio] == nullptr) {
         _calibrator[prio] = new CompassCalibrator();