diff --git a/libraries/SRV_Channel/SRV_Channel.cpp b/libraries/SRV_Channel/SRV_Channel.cpp
index dbfb1db593..735950c56e 100644
--- a/libraries/SRV_Channel/SRV_Channel.cpp
+++ b/libraries/SRV_Channel/SRV_Channel.cpp
@@ -182,3 +182,9 @@ uint16_t SRV_Channel::get_limit_pwm(LimitValue limit) const
     }
 }
 
+// return true if function is for a multicopter motor
+bool SRV_Channel::is_motor(SRV_Channel::Aux_servo_function_t function)
+{
+    return ((function >= SRV_Channel::k_motor1 && function <= SRV_Channel::k_motor8) ||
+            (function >= SRV_Channel::k_motor9 && function <= SRV_Channel::k_motor12));
+}
diff --git a/libraries/SRV_Channel/SRV_Channel.h b/libraries/SRV_Channel/SRV_Channel.h
index 1a70f5665a..7a0da141aa 100644
--- a/libraries/SRV_Channel/SRV_Channel.h
+++ b/libraries/SRV_Channel/SRV_Channel.h
@@ -110,6 +110,10 @@ public:
         k_vtail_left            = 79,
         k_vtail_right           = 80,
         k_boost_throttle        = 81,            ///< vertical booster throttle
+        k_motor9                = 82,
+        k_motor10               = 83,
+        k_motor11               = 84,
+        k_motor12               = 85,
         k_nr_aux_servo_functions         ///< This must be the last enum value (only add new values _before_ this one)
     } Aux_servo_function_t;
 
@@ -157,6 +161,9 @@ public:
         return servo_trim;
     }
 
+    // return true if function is for a multicopter motor
+    static bool is_motor(SRV_Channel::Aux_servo_function_t function);
+
 private:
     AP_Int16 servo_min;
     AP_Int16 servo_max;
diff --git a/libraries/SRV_Channel/SRV_Channel_aux.cpp b/libraries/SRV_Channel/SRV_Channel_aux.cpp
index 7a86168c0e..d57edafaf9 100644
--- a/libraries/SRV_Channel/SRV_Channel_aux.cpp
+++ b/libraries/SRV_Channel/SRV_Channel_aux.cpp
@@ -39,6 +39,7 @@ void SRV_Channel::output_ch(void)
         passthrough_from = int8_t(function - k_rcin1);
         break;
     case k_motor1 ... k_motor8:
+    case k_motor9 ... k_motor12:
         // handled by AP_Motors::rc_write()
         return;
     }