diff --git a/APMrover2/APMrover2.pde b/APMrover2/APMrover2.pde
index 54d2ee8948..1d04877134 100644
--- a/APMrover2/APMrover2.pde
+++ b/APMrover2/APMrover2.pde
@@ -669,7 +669,7 @@ static void fast_loop()
 	// ----------
 	if (g.sonar_enabled) {
 		sonar_dist_cm = sonar->read();
-        if (sonar_dist_cm <= g.sonar_trigger)  {
+        if (sonar_dist_cm <= g.sonar_trigger_cm)  {
             // obstacle detected in front 
             obstacle = true;
         } else  { 
diff --git a/APMrover2/Parameters.h b/APMrover2/Parameters.h
index ba41873bdd..cff2a7c83e 100644
--- a/APMrover2/Parameters.h
+++ b/APMrover2/Parameters.h
@@ -17,7 +17,7 @@ public:
     // The increment will prevent old parameters from being used incorrectly
     // by newer code.
     //
-    static const uint16_t k_format_version = 15;
+    static const uint16_t k_format_version = 16;
     static const uint16_t k_software_type = 20;
 
     enum {
@@ -97,8 +97,7 @@ public:
         k_param_fs_gcs_enabled,
 
         // obstacle control
-        k_param_sonar_trigger = 190,
-        k_param_sonar_enabled,
+        k_param_sonar_enabled = 190,
         k_param_sonar_type,
         k_param_sonar_trigger_cm,
         k_param_sonar_turn_angle,
@@ -203,7 +202,6 @@ public:
 	AP_Int8	    fs_gcs_enabled;
 
     // obstacle control
-    AP_Float    sonar_trigger;
     AP_Int8	    sonar_enabled;
 	AP_Int8	    sonar_type;   // 0 = XL, 1 = LV, 2 = XLL (XL with 10m
                               // range), // 3 = HRLV