diff --git a/libraries/AP_Compass/Compass.h b/libraries/AP_Compass/Compass.h
index 0755734cc9..ae115dcaa9 100644
--- a/libraries/AP_Compass/Compass.h
+++ b/libraries/AP_Compass/Compass.h
@@ -128,11 +128,11 @@ public:
 
     /// Return the current field as a Vector3f
     const Vector3f &get_field(uint8_t i) const { return _field[i]; }
-    const Vector3f &get_field(void) const { return get_field(_get_primary()); }
+    const Vector3f &get_field(void) const { return get_field(get_primary()); }
 
     /// Return the health of a compass
     bool healthy(uint8_t i) const { return _healthy[i]; }
-    bool healthy(void) const { return healthy(_get_primary()); }
+    bool healthy(void) const { return healthy(get_primary()); }
 
     /// set the current field as a Vector3f
     void set_field(const Vector3f &field) { _field[0] = field; }
@@ -142,7 +142,7 @@ public:
     /// @returns                    The current compass offsets.
     ///
     const Vector3f &get_offsets(uint8_t i) const { return _offset[i]; }
-    const Vector3f &get_offsets(void) const { return get_offsets(_get_primary()); }
+    const Vector3f &get_offsets(void) const { return get_offsets(get_primary()); }
 
     /// Sets the initial location used to get declination
     ///
@@ -215,7 +215,7 @@ public:
 
     /// get motor compensation factors as a vector
     const Vector3f& get_motor_compensation(uint8_t i) const { return _motor_compensation[i]; }
-    const Vector3f& get_motor_compensation(void) const { return get_motor_compensation(_get_primary()); }
+    const Vector3f& get_motor_compensation(void) const { return get_motor_compensation(get_primary()); }
 
     /// Saves the current motor compensation x/y/z values.
     ///
@@ -228,7 +228,7 @@ public:
     /// @returns                    The current compass offsets.
     ///
     const Vector3f &get_motor_offsets(uint8_t i) const { return _motor_offset[i]; }
-    const Vector3f &get_motor_offsets(void) const { return get_motor_offsets(_get_primary()); }
+    const Vector3f &get_motor_offsets(void) const { return get_motor_offsets(get_primary()); }
 
     /// Set the throttle as a percentage from 0.0 to 1.0
     /// @param thr_pct              throttle expressed as a percentage from 0 to 1.0
@@ -253,13 +253,18 @@ public:
     bool configured(uint8_t i);
     bool configured(void);
 
+    /// Returns the instance of the primary compass
+    ///
+    /// @returns                    the instance number of the primary compass
+    ///
+    virtual uint8_t get_primary(void) const { return 0; }
+
     static const struct AP_Param::GroupInfo var_info[];
 
     // settable parameters
     AP_Int8 _learn;                             ///<enable calibration learning
 
 protected:
-    virtual uint8_t _get_primary(void) const { return 0; }
 
     bool _healthy[COMPASS_MAX_INSTANCES];
     Vector3f _field[COMPASS_MAX_INSTANCES];     ///< magnetic field strength