diff --git a/libraries/GCS_MAVLink/GCS.h b/libraries/GCS_MAVLink/GCS.h
index 4552e97c35..a339d2a85c 100644
--- a/libraries/GCS_MAVLink/GCS.h
+++ b/libraries/GCS_MAVLink/GCS.h
@@ -158,6 +158,9 @@ public:
     void        data_stream_send(void);
     void        queued_param_send();
     void        queued_waypoint_send();
+    void        set_snoop(void (*_msg_snoop)(const mavlink_message_t* msg)) {
+        msg_snoop = _msg_snoop;
+    }
 
     static const struct AP_Param::GroupInfo        var_info[];
 
@@ -190,9 +193,6 @@ public:
     // last time we got a non-zero RSSI from RADIO_STATUS
     static uint32_t last_radio_status_remrssi_ms;
 
-    // mavlink routing object
-    static MAVLink_routing routing;
-
     // common send functions
     void send_meminfo(void);
     void send_power_status(void);
@@ -318,6 +318,12 @@ private:
     // bitmask of what mavlink channels are active
     static uint8_t mavlink_active;
 
+    // mavlink routing object
+    static MAVLink_routing routing;
+
+    // a vehicle can optionally snoop on messages for other systems
+    static void (*msg_snoop)(const mavlink_message_t* msg);
+
     // vehicle specific message send function
     bool try_send_message(enum ap_message id);
 
diff --git a/libraries/GCS_MAVLink/GCS_Common.cpp b/libraries/GCS_MAVLink/GCS_Common.cpp
index 7ec29aa386..3e787d9ca4 100644
--- a/libraries/GCS_MAVLink/GCS_Common.cpp
+++ b/libraries/GCS_MAVLink/GCS_Common.cpp
@@ -853,7 +853,11 @@ GCS_MAVLINK::update(void (*run_cli)(AP_HAL::UARTDriver *))
             // we exclude radio packets to make it possible to use the
             // CLI over the radio
             if (msg.msgid != MAVLINK_MSG_ID_RADIO && msg.msgid != MAVLINK_MSG_ID_RADIO_STATUS) {
-                mavlink_active |= (1U<<chan);
+                mavlink_active |= (1U<<(chan-MAVLINK_COMM_0));
+            }
+            // if a snoop handler has been setup then use it
+            if (msg_snoop != NULL) {
+                msg_snoop(&msg);
             }
             if (!routing.check_and_forward(chan, &msg)) {
                 handleMessage(&msg);
@@ -1099,7 +1103,7 @@ void GCS_MAVLINK::send_statustext_all(const prog_char_t *msg)
 {
     for (uint8_t i=0; i<MAVLINK_COMM_NUM_BUFFERS; i++) {
         if ((1U<<i) & mavlink_active) {
-            mavlink_channel_t chan = (mavlink_channel_t)i;
+            mavlink_channel_t chan = (mavlink_channel_t)(MAVLINK_COMM_0+i);
             if (comm_get_txspace(chan) >= MAVLINK_NUM_NON_PAYLOAD_BYTES + MAVLINK_MSG_ID_STATUSTEXT_LEN) {
                 char msg2[50];
                 strncpy_P(msg2, msg, sizeof(msg2));
diff --git a/libraries/GCS_MAVLink/GCS_MAVLink.cpp b/libraries/GCS_MAVLink/GCS_MAVLink.cpp
index 62f73a1ff6..9cbb19cc2f 100644
--- a/libraries/GCS_MAVLink/GCS_MAVLink.cpp
+++ b/libraries/GCS_MAVLink/GCS_MAVLink.cpp
@@ -46,6 +46,10 @@ static uint8_t mavlink_locked_mask;
 // routing table
 MAVLink_routing GCS_MAVLINK::routing;
 
+// snoop function for vehicle types that want to see messages for
+// other targets
+void (*GCS_MAVLINK::msg_snoop)(const mavlink_message_t* msg) = NULL;
+
 /*
   lock a channel, preventing use by MAVLink
  */