diff --git a/libraries/AP_HAL_AVR_SITL/SITL_State.cpp b/libraries/AP_HAL_AVR_SITL/SITL_State.cpp
index 094fec63eb..643f26465f 100644
--- a/libraries/AP_HAL_AVR_SITL/SITL_State.cpp
+++ b/libraries/AP_HAL_AVR_SITL/SITL_State.cpp
@@ -103,7 +103,7 @@ void SITL_State::_parse_command_line(int argc, char * const argv[])
     setvbuf(stdout, (char *)0, _IONBF, 0);
     setvbuf(stderr, (char *)0, _IONBF, 0);
 
-	while ((opt = getopt(argc, argv, "swhr:H:CI:")) != -1) {
+	while ((opt = getopt(argc, argv, "swhr:H:CI:P:")) != -1) {
 		switch (opt) {
 		case 'w':
 			AP_Param::erase_all();
@@ -125,6 +125,9 @@ void SITL_State::_parse_command_line(int argc, char * const argv[])
             _simin_port += instance * 10;
         }
 			break;
+		case 'P':
+            _set_param_default(optarg);
+			break;
 		default:
 			_usage();
 			exit(1);
@@ -156,6 +159,37 @@ void SITL_State::_parse_command_line(int argc, char * const argv[])
 }
 
 
+void SITL_State::_set_param_default(char *parm)
+{
+    char *p = strchr(parm, '=');
+    if (p == NULL) {
+        printf("Please specify parameter as NAME=VALUE");
+        exit(1);
+    }
+    float value = atof(p+1);
+    *p = 0;
+    enum ap_var_type var_type;
+    AP_Param *vp = AP_Param::find(parm, &var_type);
+    if (vp == NULL) {
+        printf("Unknown parameter %s\n", parm);
+        exit(1);        
+    }
+    if (var_type == AP_PARAM_FLOAT) {
+        ((AP_Float *)vp)->set_and_save(value);
+    } else if (var_type == AP_PARAM_INT32) {
+        ((AP_Int32 *)vp)->set_and_save(value);
+    } else if (var_type == AP_PARAM_INT16) {
+        ((AP_Int16 *)vp)->set_and_save(value);
+    } else if (var_type == AP_PARAM_INT8) {
+        ((AP_Int8 *)vp)->set_and_save(value);
+    } else {
+        printf("Unable to set parameter %s\n", parm);
+        exit(1);
+    }
+    printf("Set parameter %s to %f\n", parm, value);
+}
+
+
 /*
   setup for SITL handling
  */
diff --git a/libraries/AP_HAL_AVR_SITL/SITL_State.h b/libraries/AP_HAL_AVR_SITL/SITL_State.h
index a35f2050e4..aa2d146693 100644
--- a/libraries/AP_HAL_AVR_SITL/SITL_State.h
+++ b/libraries/AP_HAL_AVR_SITL/SITL_State.h
@@ -51,6 +51,7 @@ public:
 
 private:
     void _parse_command_line(int argc, char * const argv[]);
+    void _set_param_default(char *parm);
     void _usage(void);
     void _sitl_setup(void);
     void _setup_fdm(void);