diff --git a/ArduPlane/Log.cpp b/ArduPlane/Log.cpp
index 8f7f17c987..36b56a2ad4 100644
--- a/ArduPlane/Log.cpp
+++ b/ArduPlane/Log.cpp
@@ -186,7 +186,8 @@ struct PACKED log_Sonar {
     float correction;
 };
 
-// Write a sonar packet
+// Write a sonar packet.  Note that RFND log messages are written by
+// RangeFinder itself as part of update().
 void Plane::Log_Write_Sonar()
 {
     uint16_t distance = 0;
@@ -203,8 +204,6 @@ void Plane::Log_Write_Sonar()
         correction  : rangefinder_state.correction
     };
     logger.WriteBlock(&pkt, sizeof(pkt));
-
-    logger.Write_RFND(rangefinder);
 }
 
 struct PACKED log_Arm_Disarm {
diff --git a/ArduPlane/system.cpp b/ArduPlane/system.cpp
index 374d28f1a9..8da369aad5 100644
--- a/ArduPlane/system.cpp
+++ b/ArduPlane/system.cpp
@@ -87,6 +87,7 @@ void Plane::init_ardupilot()
     barometer.init();
 
     // initialise rangefinder
+    rangefinder.set_log_rfnd_bit(MASK_LOG_SONAR);
     rangefinder.init(ROTATION_PITCH_270);
 
     // initialise battery monitoring