diff --git a/libraries/SITL/SIM_Aircraft.cpp b/libraries/SITL/SIM_Aircraft.cpp
index 13828d49f5..ae20f0c989 100644
--- a/libraries/SITL/SIM_Aircraft.cpp
+++ b/libraries/SITL/SIM_Aircraft.cpp
@@ -390,7 +390,7 @@ void Aircraft::fill_fdm(struct sitl_fdm &fdm)
     fdm.velocity_air_bf = velocity_air_bf;
     fdm.battery_voltage = battery_voltage;
     fdm.battery_current = battery_current;
-    fdm.motor_mask = motor_mask;
+    fdm.motor_mask = motor_mask | sitl->vibe_motor_mask;
     memcpy(fdm.rpm, rpm, sizeof(fdm.rpm));
     fdm.rcin_chan_count = rcin_chan_count;
     fdm.range = rangefinder_range();
diff --git a/libraries/SITL/SITL.cpp b/libraries/SITL/SITL.cpp
index 9689d1e92d..0ca255e9fe 100644
--- a/libraries/SITL/SITL.cpp
+++ b/libraries/SITL/SITL.cpp
@@ -174,6 +174,9 @@ const AP_Param::GroupInfo SIM::var_info2[] = {
     // motor harmonics
     AP_GROUPINFO("VIB_MOT_HMNC", 60, SIM,  vibe_motor_harmonics, 1),
 
+    // motor mask, allowing external simulators to mark motors
+    AP_GROUPINFO("VIB_MOT_MASK", 5, SIM,  vibe_motor_mask, 0),
+    
     // max motor vibration frequency
     AP_GROUPINFO("VIB_MOT_MAX", 61, SIM,  vibe_motor, 0.0f),
     // minimum throttle for simulated ins noise
diff --git a/libraries/SITL/SITL.h b/libraries/SITL/SITL.h
index cacc89875b..d201d9046b 100644
--- a/libraries/SITL/SITL.h
+++ b/libraries/SITL/SITL.h
@@ -336,6 +336,9 @@ public:
     // what harmonics to generate
     AP_Int16 vibe_motor_harmonics;
 
+    // what servos are motors
+    AP_Int32 vibe_motor_mask;
+    
     // minimum throttle for addition of ins noise
     AP_Float ins_noise_throttle_min;