diff --git a/libraries/AP_RangeFinder/AP_RangeFinder.cpp b/libraries/AP_RangeFinder/AP_RangeFinder.cpp
index 4cd9dae559..7ffb3779b5 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder.cpp
@@ -314,7 +314,7 @@ void RangeFinder::update(void)
 #endif
 }
 
-bool RangeFinder::_add_backend(AP_RangeFinder_Backend *backend, uint8_t instance)
+bool RangeFinder::_add_backend(AP_RangeFinder_Backend *backend, uint8_t instance, uint8_t serial_instance)
 {
     if (!backend) {
         return false;
@@ -326,7 +326,7 @@ bool RangeFinder::_add_backend(AP_RangeFinder_Backend *backend, uint8_t instance
         // we've allocated the same instance twice
         INTERNAL_ERROR(AP_InternalError::error_t::flow_of_control);
     }
-
+    backend->init_serial(serial_instance);
     drivers[instance] = backend;
     num_instances = MAX(num_instances, instance+1);
 
@@ -442,17 +442,17 @@ void RangeFinder::detect_instance(uint8_t instance, uint8_t& serial_instance)
         break;
     case Type::LWSER:
         if (AP_RangeFinder_LightWareSerial::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_LightWareSerial(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_LightWareSerial(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::LEDDARONE:
         if (AP_RangeFinder_LeddarOne::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_LeddarOne(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_LeddarOne(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::ULANDING:
         if (AP_RangeFinder_uLanding::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_uLanding(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_uLanding(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::BEBOP:
@@ -472,7 +472,7 @@ void RangeFinder::detect_instance(uint8_t instance, uint8_t& serial_instance)
         break;
     case Type::MBSER:
         if (AP_RangeFinder_MaxsonarSerialLV::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_MaxsonarSerialLV(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_MaxsonarSerialLV(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::ANALOG:
@@ -493,27 +493,27 @@ void RangeFinder::detect_instance(uint8_t instance, uint8_t& serial_instance)
         break;
     case Type::NMEA:
         if (AP_RangeFinder_NMEA::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_NMEA(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_NMEA(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::WASP:
         if (AP_RangeFinder_Wasp::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_Wasp(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_Wasp(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::BenewakeTF02:
         if (AP_RangeFinder_Benewake_TF02::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_Benewake_TF02(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_Benewake_TF02(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::BenewakeTFmini:
         if (AP_RangeFinder_Benewake_TFMini::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_Benewake_TFMini(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_Benewake_TFMini(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::BenewakeTF03:
         if (AP_RangeFinder_Benewake_TF03::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_Benewake_TF03(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_Benewake_TF03(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::PWM:
@@ -525,17 +525,17 @@ void RangeFinder::detect_instance(uint8_t instance, uint8_t& serial_instance)
         break;
     case Type::BLPing:
         if (AP_RangeFinder_BLPing::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_BLPing(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_BLPing(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::Lanbao:
         if (AP_RangeFinder_Lanbao::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_Lanbao(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_Lanbao(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
     case Type::LeddarVu8_Serial:
         if (AP_RangeFinder_LeddarVu8::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_LeddarVu8(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_LeddarVu8(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
 
@@ -552,7 +552,7 @@ void RangeFinder::detect_instance(uint8_t instance, uint8_t& serial_instance)
 
     case Type::GYUS42v2:
         if (AP_RangeFinder_GYUS42v2::detect(serial_instance)) {
-            _add_backend(new AP_RangeFinder_GYUS42v2(state[instance], params[instance], serial_instance++), instance);
+            _add_backend(new AP_RangeFinder_GYUS42v2(state[instance], params[instance]), instance, serial_instance++);
         }
         break;
 
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder.h b/libraries/AP_RangeFinder/AP_RangeFinder.h
index 6e264e4c6b..b1cd63545e 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder.h
@@ -212,7 +212,7 @@ private:
 
     void detect_instance(uint8_t instance, uint8_t& serial_instance);
 
-    bool _add_backend(AP_RangeFinder_Backend *driver, uint8_t instance);
+    bool _add_backend(AP_RangeFinder_Backend *driver, uint8_t instance, uint8_t serial_instance=0);
 
     uint32_t _log_rfnd_bit = -1;
     void Log_RFND() const;
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h b/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h
index 873a615859..97a265fdec 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_Backend.h
@@ -30,6 +30,7 @@ public:
 
     // update the state structure
     virtual void update() = 0;
+    virtual void init_serial(uint8_t serial_instance) {};
 
     virtual void handle_msg(const mavlink_message_t &msg) { return; }
 #if HAL_MSP_RANGEFINDER_ENABLED
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.cpp
index 4f9eaee0b2..50cc913dd0 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.cpp
@@ -28,9 +28,13 @@ extern const AP_HAL::HAL& hal;
 */
 AP_RangeFinder_Backend_Serial::AP_RangeFinder_Backend_Serial(
     RangeFinder::RangeFinder_State &_state,
-    AP_RangeFinder_Params &_params,
-    uint8_t serial_instance) :
+    AP_RangeFinder_Params &_params) :
     AP_RangeFinder_Backend(_state, _params)
+{
+
+}
+
+void AP_RangeFinder_Backend_Serial::init_serial(uint8_t serial_instance)
 {
     uart = AP::serialmanager().find_serial(AP_SerialManager::SerialProtocol_Rangefinder, serial_instance);
     if (uart != nullptr) {
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.h b/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.h
index b8b6123c34..8fb67c2ff8 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_Backend_Serial.h
@@ -7,9 +7,9 @@ class AP_RangeFinder_Backend_Serial : public AP_RangeFinder_Backend
 public:
     // constructor
     AP_RangeFinder_Backend_Serial(RangeFinder::RangeFinder_State &_state,
-                                  AP_RangeFinder_Params &_params,
-                                  uint8_t serial_instance);
+                                  AP_RangeFinder_Params &_params);
 
+    void init_serial(uint8_t serial_instance) override;
     // static detection function
     static bool detect(uint8_t serial_instance);
 
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.cpp
index 56d11fcd30..6da29e7d3c 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.cpp
@@ -67,9 +67,8 @@ const AP_Param::GroupInfo AP_RangeFinder_Wasp::var_info[] = {
 };
 
 AP_RangeFinder_Wasp::AP_RangeFinder_Wasp(RangeFinder::RangeFinder_State &_state,
-                                         AP_RangeFinder_Params &_params,
-                                         uint8_t serial_instance) :
-    AP_RangeFinder_Backend_Serial(_state, _params, serial_instance)
+                                         AP_RangeFinder_Params &_params) :
+    AP_RangeFinder_Backend_Serial(_state, _params)
 {
     AP_Param::setup_object_defaults(this, var_info);
 
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.h b/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.h
index 2c8e5d9674..2ccc2bd33f 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_Wasp.h
@@ -10,8 +10,7 @@ class AP_RangeFinder_Wasp : public AP_RangeFinder_Backend_Serial {
 
 public:
     AP_RangeFinder_Wasp(RangeFinder::RangeFinder_State &_state,
-                        AP_RangeFinder_Params &_params,
-                        uint8_t serial_instance);
+                        AP_RangeFinder_Params &_params);
 
     void update(void) override;