diff --git a/ArduSub/GCS_Mavlink.cpp b/ArduSub/GCS_Mavlink.cpp
index 8d80faf1bd..e289e8a41f 100644
--- a/ArduSub/GCS_Mavlink.cpp
+++ b/ArduSub/GCS_Mavlink.cpp
@@ -428,6 +428,11 @@ void Sub::send_pid_tuning(mavlink_channel_t chan)
     }
 }
 
+uint8_t GCS_MAVLINK_Sub::sysid_my_gcs() const
+{
+    return sub.g.sysid_my_gcs;
+}
+
 // try to send a message, return false if it won't fit in the serial tx buffer
 bool GCS_MAVLINK_Sub::try_send_message(enum ap_message id)
 {
diff --git a/ArduSub/GCS_Mavlink.h b/ArduSub/GCS_Mavlink.h
index e343ccf893..28f1c0fdfd 100644
--- a/ArduSub/GCS_Mavlink.h
+++ b/ArduSub/GCS_Mavlink.h
@@ -15,6 +15,7 @@ protected:
     };
 
     AP_Mission *get_mission() override;
+    uint8_t sysid_my_gcs() const override;
 
 private: