diff --git a/libraries/AP_GPS/AP_GPS_ERB.cpp b/libraries/AP_GPS/AP_GPS_ERB.cpp
index 979bda5072..a1be658010 100644
--- a/libraries/AP_GPS/AP_GPS_ERB.cpp
+++ b/libraries/AP_GPS/AP_GPS_ERB.cpp
@@ -32,12 +32,6 @@ extern const AP_HAL::HAL& hal;
  # define Debug(fmt, args ...)
 #endif
 
-AP_GPS_ERB::AP_GPS_ERB(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
-    AP_GPS_Backend(_gps, _state, _port),
-    next_fix(AP_GPS::NO_FIX)
-{
-}
-
 // Process bytes available from the stream
 //
 // The stream is assumed to contain only messages we recognise.  If it
diff --git a/libraries/AP_GPS/AP_GPS_ERB.h b/libraries/AP_GPS/AP_GPS_ERB.h
index 8eacac6729..69fde51d69 100644
--- a/libraries/AP_GPS/AP_GPS_ERB.h
+++ b/libraries/AP_GPS/AP_GPS_ERB.h
@@ -27,7 +27,8 @@
 class AP_GPS_ERB : public AP_GPS_Backend
 {
 public:
-    AP_GPS_ERB(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
+
+    using AP_GPS_Backend::AP_GPS_Backend;
 
     // Methods
     bool read() override;
@@ -150,5 +151,5 @@ private:
     bool _parse_gps();
 
     // used to update fix between status and position packets
-    AP_GPS::GPS_Status next_fix;
+    AP_GPS::GPS_Status next_fix = AP_GPS::NO_FIX;
 };
diff --git a/libraries/AP_GPS/AP_GPS_MTK.cpp b/libraries/AP_GPS/AP_GPS_MTK.cpp
index 10b9557204..ae55765867 100644
--- a/libraries/AP_GPS/AP_GPS_MTK.cpp
+++ b/libraries/AP_GPS/AP_GPS_MTK.cpp
@@ -28,9 +28,7 @@
 const char AP_GPS_MTK::_initialisation_blob[] = MTK_OUTPUT_5HZ SBAS_ON WAAS_ON MTK_NAVTHRES_OFF;
 
 AP_GPS_MTK::AP_GPS_MTK(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
-    AP_GPS_Backend(_gps, _state, _port),
-    _step(0),
-    _payload_counter(0)
+    AP_GPS_Backend(_gps, _state, _port)
 {
     gps.send_blob_start(state.instance, _initialisation_blob, sizeof(_initialisation_blob));
 }
diff --git a/libraries/AP_GPS/AP_GPS_NMEA.cpp b/libraries/AP_GPS/AP_GPS_NMEA.cpp
index a24c2b70c2..1ec6120f1d 100644
--- a/libraries/AP_GPS/AP_GPS_NMEA.cpp
+++ b/libraries/AP_GPS/AP_GPS_NMEA.cpp
@@ -50,13 +50,6 @@ extern const AP_HAL::HAL& hal;
 #define DIGIT_TO_VAL(_x)        (_x - '0')
 #define hexdigit(x) ((x)>9?'A'+((x)-10):'0'+(x))
 
-AP_GPS_NMEA::AP_GPS_NMEA(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
-    AP_GPS_Backend(_gps, _state, _port)
-{
-    // this guarantees that _term is always null terminated
-    memset(_term, 0, sizeof(_term));
-}
-
 bool AP_GPS_NMEA::read(void)
 {
     int16_t numc;
diff --git a/libraries/AP_GPS/AP_GPS_NMEA.h b/libraries/AP_GPS/AP_GPS_NMEA.h
index 31c35e207e..a7f982902e 100644
--- a/libraries/AP_GPS/AP_GPS_NMEA.h
+++ b/libraries/AP_GPS/AP_GPS_NMEA.h
@@ -53,7 +53,8 @@ class AP_GPS_NMEA : public AP_GPS_Backend
     friend class AP_GPS_NMEA_Test;
 
 public:
-	AP_GPS_NMEA(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
+
+    using AP_GPS_Backend::AP_GPS_Backend;
 
     /// Checks the serial receive buffer for characters,
     /// attempts to parse NMEA data and updates internal state