diff --git a/libraries/SITL/SITL.cpp b/libraries/SITL/SITL.cpp
index dac247bddd..87c0249648 100644
--- a/libraries/SITL/SITL.cpp
+++ b/libraries/SITL/SITL.cpp
@@ -60,6 +60,7 @@ const AP_Param::GroupInfo SITL::var_info[] PROGMEM = {
     AP_GROUPINFO("MAG_MOT",       29, SITL,  mag_mot, 0),
     AP_GROUPINFO("ACC_BIAS",      30, SITL,  accel_bias, 0),
     AP_GROUPINFO("BARO_GLITCH",   31, SITL,  baro_glitch, 0),
+    AP_GROUPINFO("SONAR_SCALE",   32, SITL,  sonar_scale, 12.1212f),
     AP_GROUPEND
 };
 
diff --git a/libraries/SITL/SITL.h b/libraries/SITL/SITL.h
index 62a4acc03d..4758593a94 100644
--- a/libraries/SITL/SITL.h
+++ b/libraries/SITL/SITL.h
@@ -63,6 +63,7 @@ public:
 
     AP_Float sonar_glitch;// probablility between 0-1 that any given sonar sample will read as max distance
     AP_Float sonar_noise; // in metres
+    AP_Float sonar_scale; // meters per volt
 
 	AP_Float drift_speed; // degrees/second/minute
 	AP_Float drift_time;  // period in minutes