diff --git a/libraries/AP_Proximity/AP_Proximity_AirSimSITL.cpp b/libraries/AP_Proximity/AP_Proximity_AirSimSITL.cpp
index fcf0dbec5a..44a1efde9d 100644
--- a/libraries/AP_Proximity/AP_Proximity_AirSimSITL.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_AirSimSITL.cpp
@@ -23,16 +23,6 @@ extern const AP_HAL::HAL& hal;
 #define PROXIMITY_MAX_RANGE 100.0f
 #define PROXIMITY_ACCURACY 0.1f
 
-/* 
-   The constructor also initialises the proximity sensor. 
-*/
-AP_Proximity_AirSimSITL::AP_Proximity_AirSimSITL(AP_Proximity &_frontend,
-                                     AP_Proximity::Proximity_State &_state):
-    AP_Proximity_Backend(_frontend, _state),
-    sitl(AP::sitl())
-{
-}
-
 // update the state of the sensor
 void AP_Proximity_AirSimSITL::update(void)
 {
diff --git a/libraries/AP_Proximity/AP_Proximity_AirSimSITL.h b/libraries/AP_Proximity/AP_Proximity_AirSimSITL.h
index b398417cd4..c2edf94888 100644
--- a/libraries/AP_Proximity/AP_Proximity_AirSimSITL.h
+++ b/libraries/AP_Proximity/AP_Proximity_AirSimSITL.h
@@ -26,7 +26,7 @@ class AP_Proximity_AirSimSITL : public AP_Proximity_Backend
 
 public:
     // constructor
-    AP_Proximity_AirSimSITL(AP_Proximity &_frontend, AP_Proximity::Proximity_State &_state);
+    using AP_Proximity_Backend::AP_Proximity_Backend;
 
     // update state
     void update(void) override;
@@ -39,6 +39,6 @@ public:
     bool get_upward_distance(float &distance) const override;
 
 private:
-    SITL::SITL *sitl;
+    SITL::SITL *sitl = AP::sitl();
 };
 #endif // CONFIG_HAL_BOARD
diff --git a/libraries/AP_Proximity/AP_Proximity_MAV.cpp b/libraries/AP_Proximity/AP_Proximity_MAV.cpp
index 428fe7f0b4..e764e25ffb 100644
--- a/libraries/AP_Proximity/AP_Proximity_MAV.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_MAV.cpp
@@ -23,17 +23,6 @@ extern const AP_HAL::HAL& hal;
 
 #define PROXIMITY_MAV_TIMEOUT_MS    500 // distance messages must arrive within this many milliseconds
 
-/* 
-   The constructor also initialises the proximity sensor. Note that this
-   constructor is not called until detect() returns true, so we
-   already know that we should setup the proximity sensor
-*/
-AP_Proximity_MAV::AP_Proximity_MAV(AP_Proximity &_frontend,
-                                   AP_Proximity::Proximity_State &_state) :
-    AP_Proximity_Backend(_frontend, _state)
-{
-}
-
 // update the state of the sensor
 void AP_Proximity_MAV::update(void)
 {
diff --git a/libraries/AP_Proximity/AP_Proximity_MAV.h b/libraries/AP_Proximity/AP_Proximity_MAV.h
index 26e0f698fa..af8360fa46 100644
--- a/libraries/AP_Proximity/AP_Proximity_MAV.h
+++ b/libraries/AP_Proximity/AP_Proximity_MAV.h
@@ -8,7 +8,7 @@ class AP_Proximity_MAV : public AP_Proximity_Backend
 
 public:
     // constructor
-    AP_Proximity_MAV(AP_Proximity &_frontend, AP_Proximity::Proximity_State &_state);
+    using AP_Proximity_Backend::AP_Proximity_Backend;
 
     // update state
     void update(void) override;
diff --git a/libraries/AP_Proximity/AP_Proximity_MorseSITL.cpp b/libraries/AP_Proximity/AP_Proximity_MorseSITL.cpp
index 1cd54d370d..42f0c15444 100644
--- a/libraries/AP_Proximity/AP_Proximity_MorseSITL.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_MorseSITL.cpp
@@ -24,16 +24,6 @@ extern const AP_HAL::HAL& hal;
 #define PROXIMITY_MAX_RANGE 200.0f
 #define PROXIMITY_ACCURACY 0.1f
 
-/* 
-   The constructor also initialises the proximity sensor. 
-*/
-AP_Proximity_MorseSITL::AP_Proximity_MorseSITL(AP_Proximity &_frontend,
-                                     AP_Proximity::Proximity_State &_state):
-    AP_Proximity_Backend(_frontend, _state),
-    sitl(AP::sitl())
-{
-}
-
 // update the state of the sensor
 void AP_Proximity_MorseSITL::update(void)
 {
diff --git a/libraries/AP_Proximity/AP_Proximity_MorseSITL.h b/libraries/AP_Proximity/AP_Proximity_MorseSITL.h
index 412e92e168..5d107e19b6 100644
--- a/libraries/AP_Proximity/AP_Proximity_MorseSITL.h
+++ b/libraries/AP_Proximity/AP_Proximity_MorseSITL.h
@@ -11,7 +11,7 @@ class AP_Proximity_MorseSITL : public AP_Proximity_Backend
 
 public:
     // constructor
-    AP_Proximity_MorseSITL(AP_Proximity &_frontend, AP_Proximity::Proximity_State &_state);
+    using AP_Proximity_Backend::AP_Proximity_Backend;
 
     // update state
     void update(void) override;
@@ -24,7 +24,7 @@ public:
     bool get_upward_distance(float &distance) const override;
 
 private:
-    SITL::SITL *sitl;
+    SITL::SITL *sitl = AP::sitl();
     float distance_maximum;
 };
 #endif // CONFIG_HAL_BOARD
diff --git a/libraries/AP_Proximity/AP_Proximity_RangeFinder.cpp b/libraries/AP_Proximity/AP_Proximity_RangeFinder.cpp
index 229c974eb1..46c1ac833d 100644
--- a/libraries/AP_Proximity/AP_Proximity_RangeFinder.cpp
+++ b/libraries/AP_Proximity/AP_Proximity_RangeFinder.cpp
@@ -20,15 +20,6 @@
 #include <AP_RangeFinder/AP_RangeFinder.h>
 #include <AP_RangeFinder/RangeFinder_Backend.h>
 
-extern const AP_HAL::HAL& hal;
-
-AP_Proximity_RangeFinder::AP_Proximity_RangeFinder(AP_Proximity &_frontend,
-                                   AP_Proximity::Proximity_State &_state) :
-    AP_Proximity_Backend(_frontend, _state),
-    _distance_upward(-1)
-{
-}
-
 // update the state of the sensor
 void AP_Proximity_RangeFinder::update(void)
 {
diff --git a/libraries/AP_Proximity/AP_Proximity_RangeFinder.h b/libraries/AP_Proximity/AP_Proximity_RangeFinder.h
index f6d7ed59f5..e624f0c70e 100644
--- a/libraries/AP_Proximity/AP_Proximity_RangeFinder.h
+++ b/libraries/AP_Proximity/AP_Proximity_RangeFinder.h
@@ -10,7 +10,7 @@ class AP_Proximity_RangeFinder : public AP_Proximity_Backend
 
 public:
     // constructor
-    AP_Proximity_RangeFinder(AP_Proximity &_frontend, AP_Proximity::Proximity_State &_state);
+    using AP_Proximity_Backend::AP_Proximity_Backend;
 
     // update state
     void update(void) override;
@@ -31,5 +31,5 @@ private:
 
     // upward distance support
     uint32_t _last_upward_update_ms;    // system time of last update distance
-    float _distance_upward;             // upward distance in meters, negative if the last reading was out of range
+    float _distance_upward = -1;        // upward distance in meters, negative if the last reading was out of range
 };