diff --git a/sw/airborne/subsystems/ahrs.c b/sw/airborne/subsystems/ahrs.c
index 8bc6c38203..f67191375c 100644
--- a/sw/airborne/subsystems/ahrs.c
+++ b/sw/airborne/subsystems/ahrs.c
@@ -29,3 +29,13 @@
 
 struct Ahrs ahrs;
 
+#define WEAK __attribute__((weak))
+// weak functions, used if not explicitly provided by implementation
+
+void WEAK ahrs_propagate(void) {}
+
+void WEAK ahrs_update_accel(void) {}
+
+void WEAK ahrs_update_mag(void) {}
+
+void WEAK ahrs_update_gps(void) {}
diff --git a/sw/airborne/subsystems/ahrs.h b/sw/airborne/subsystems/ahrs.h
index 5c49dcf710..15d39990d1 100644
--- a/sw/airborne/subsystems/ahrs.h
+++ b/sw/airborne/subsystems/ahrs.h
@@ -61,25 +61,25 @@ extern void ahrs_align(void);
 
 /** Propagation. Usually integrates the gyro rates to angles.
  *  Reads the global #imu data struct.
- *  Needs to be implemented by each AHRS algorithm.
+ *  Does nothing if not implemented by specific AHRS algorithm.
  */
 extern void ahrs_propagate(void);
 
 /** Update AHRS state with accerleration measurements.
  *  Reads the global #imu data struct.
- *  Needs to be implemented by each AHRS algorithm.
+ *  Does nothing if not implemented by specific AHRS algorithm.
  */
 extern void ahrs_update_accel(void);
 
 /** Update AHRS state with magnetometer measurements.
  *  Reads the global #imu data struct.
- *  Needs to be implemented by each AHRS algorithm.
+ *  Does nothing if not implemented by specific AHRS algorithm.
  */
 extern void ahrs_update_mag(void);
 
 /** Update AHRS state with GPS measurements.
  *  Reads the global #gps data struct.
- *  Needs to be implemented by each AHRS algorithm.
+ *  Does nothing if not implemented by specific AHRS algorithm.
  */
 extern void ahrs_update_gps(void);
 
diff --git a/sw/airborne/subsystems/ahrs/ahrs_ardrone2.c b/sw/airborne/subsystems/ahrs/ahrs_ardrone2.c
index 29fb02b165..3c6eb71a73 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_ardrone2.c
+++ b/sw/airborne/subsystems/ahrs/ahrs_ardrone2.c
@@ -195,22 +195,8 @@ void ahrs_propagate(void) {
   }
 }
 
-void ahrs_update_accel(void) {
-
-}
-
-void ahrs_update_mag(void) {
-
-}
-
-void ahrs_update_gps(void) {
-
-}
-
 void ahrs_aligner_init(void) {
-
 }
 
 void ahrs_aligner_run(void) {
-
 }
diff --git a/sw/airborne/subsystems/ahrs/ahrs_float_mlkf.c b/sw/airborne/subsystems/ahrs/ahrs_float_mlkf.c
index 1ae27fc631..33ed755eaa 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_float_mlkf.c
+++ b/sw/airborne/subsystems/ahrs/ahrs_float_mlkf.c
@@ -125,9 +125,6 @@ void ahrs_propagate(void) {
   set_body_state_from_quat();
 }
 
-void ahrs_update_gps(void) {
-}
-
 void ahrs_update_accel(void) {
   struct FloatVect3 imu_g;
   ACCELS_FLOAT_OF_BFP(imu_g, imu.accel);
diff --git a/sw/airborne/subsystems/ahrs/ahrs_gx3.c b/sw/airborne/subsystems/ahrs/ahrs_gx3.c
index cb8f1681f3..052018a9b2 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_gx3.c
+++ b/sw/airborne/subsystems/ahrs/ahrs_gx3.c
@@ -347,14 +347,3 @@ void ahrs_aligner_run(void) {
 void ahrs_aligner_init(void) {
 }
 
-void ahrs_propagate(void) {
-}
-
-void ahrs_update_accel(void) {
-}
-
-void ahrs_update_mag(void) {
-}
-
-void ahrs_update_gps(void) {
-}
diff --git a/sw/airborne/subsystems/ahrs/ahrs_infrared.c b/sw/airborne/subsystems/ahrs/ahrs_infrared.c
index 267b2245d3..991718b743 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_infrared.c
+++ b/sw/airborne/subsystems/ahrs/ahrs_infrared.c
@@ -87,11 +87,6 @@ void ahrs_propagate(void) {
   stateSetBodyRates_f(&body_rate);
 }
 
-void ahrs_update_accel(void) {
-}
-
-void ahrs_update_mag(void) {
-}
 
 void ahrs_update_gps(void) {
 
diff --git a/sw/airborne/subsystems/ahrs/ahrs_int_cmpl_euler.c b/sw/airborne/subsystems/ahrs/ahrs_int_cmpl_euler.c
index 2becf1456b..c676cb16fd 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_int_cmpl_euler.c
+++ b/sw/airborne/subsystems/ahrs/ahrs_int_cmpl_euler.c
@@ -278,10 +278,6 @@ void ahrs_update_mag(void) {
 
 }
 
-void ahrs_update_gps(void) {
-
-}
-
 /* measures phi and theta assuming no dynamic acceleration ?!! */
 __attribute__ ((always_inline)) static inline void get_phi_theta_measurement_fom_accel(int32_t* phi_meas, int32_t* theta_meas, struct Int32Vect3 accel) {
 
diff --git a/sw/airborne/subsystems/ahrs/ahrs_sim.c b/sw/airborne/subsystems/ahrs/ahrs_sim.c
index b5f6bc11cf..5c1d5c726f 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_sim.c
+++ b/sw/airborne/subsystems/ahrs/ahrs_sim.c
@@ -94,13 +94,3 @@ void ahrs_propagate(void) {
   }
 }
 
-void ahrs_update_accel(void) {
-}
-
-void ahrs_update_mag(void) {
-}
-
-void ahrs_update_gps(void) {
-
-}
-