diff --git a/libraries/AC_AutoTune/AC_AutoTune_Heli.h b/libraries/AC_AutoTune/AC_AutoTune_Heli.h
index 133047a12db06..9ba8596897795 100644
--- a/libraries/AC_AutoTune/AC_AutoTune_Heli.h
+++ b/libraries/AC_AutoTune/AC_AutoTune_Heli.h
@@ -20,6 +20,7 @@
 
 #include "AC_AutoTune.h"
 #include <AP_Math/chirp.h>
+#include <GCS_MAVLink/GCS.h>
 
 #include <AP_Scheduler/AP_Scheduler.h>
 
diff --git a/libraries/AP_CANManager/AP_CANManager.cpp b/libraries/AP_CANManager/AP_CANManager.cpp
index b51a0d15c9ee3..dd96372ac03a9 100644
--- a/libraries/AP_CANManager/AP_CANManager.cpp
+++ b/libraries/AP_CANManager/AP_CANManager.cpp
@@ -30,7 +30,7 @@
 #include <AP_PiccoloCAN/AP_PiccoloCAN.h>
 #include <AP_EFI/AP_EFI_NWPMU.h>
 #include "AP_CANTester.h"
-#include <GCS_MAVLink/GCS_MAVLink.h>
+#include <GCS_MAVLink/GCS.h>
 #if CONFIG_HAL_BOARD == HAL_BOARD_LINUX
 #include <AP_HAL_Linux/CANSocketIface.h>
 #elif CONFIG_HAL_BOARD == HAL_BOARD_SITL
diff --git a/libraries/AP_CANManager/AP_CANManager.h b/libraries/AP_CANManager/AP_CANManager.h
index fb4dccd217384..26fbe27b6662e 100644
--- a/libraries/AP_CANManager/AP_CANManager.h
+++ b/libraries/AP_CANManager/AP_CANManager.h
@@ -24,7 +24,10 @@
 #include <AP_Param/AP_Param.h>
 #include "AP_SLCANIface.h"
 #include "AP_CANDriver.h"
-#include <GCS_MAVLink/GCS.h>
+#include <GCS_MAVLink/GCS_config.h>
+#if HAL_GCS_ENABLED
+#include <GCS_MAVLink/GCS_MAVLink.h>
+#endif
 
 class AP_CANManager
 {
diff --git a/libraries/AP_CANManager/AP_CANTester_KDECAN.cpp b/libraries/AP_CANManager/AP_CANTester_KDECAN.cpp
index 5afe1665767e5..a3e7ea979aadf 100644
--- a/libraries/AP_CANManager/AP_CANTester_KDECAN.cpp
+++ b/libraries/AP_CANManager/AP_CANTester_KDECAN.cpp
@@ -25,6 +25,7 @@
 #include <AP_Math/AP_Math.h>
 #include <AP_HAL/utility/sparse-endian.h>
 #include <AP_Vehicle/AP_Vehicle_Type.h>
+#include <GCS_MAVLink/GCS.h>
 
 #define debug_can(level_debug, fmt, args...) do { AP::can().log_text(level_debug, "TestKDECAN",  fmt, ##args); } while (0)
 extern const AP_HAL::HAL& hal;
diff --git a/libraries/AP_CANManager/AP_SLCANIface.cpp b/libraries/AP_CANManager/AP_SLCANIface.cpp
index df1327c9ed815..8c11ffdccc08f 100644
--- a/libraries/AP_CANManager/AP_SLCANIface.cpp
+++ b/libraries/AP_CANManager/AP_SLCANIface.cpp
@@ -28,6 +28,7 @@
 #include <AP_SerialManager/AP_SerialManager.h>
 #include <stdio.h>
 #include <AP_Vehicle/AP_Vehicle_Type.h>
+#include <GCS_MAVLink/GCS.h>
 
 #define LOG_TAG "SLCAN"
 
diff --git a/libraries/AP_CheckFirmware/AP_CheckFirmware.h b/libraries/AP_CheckFirmware/AP_CheckFirmware.h
index cf0837d20cab0..648994fe292f8 100644
--- a/libraries/AP_CheckFirmware/AP_CheckFirmware.h
+++ b/libraries/AP_CheckFirmware/AP_CheckFirmware.h
@@ -6,8 +6,9 @@
 #include <AP_HAL/AP_HAL_Boards.h>
 #include <AP_OpenDroneID/AP_OpenDroneID_config.h>
 #include <AP_HAL/AP_HAL.h>
-#ifndef HAL_BOOTLOADER_BUILD
-#include <GCS_MAVLink/GCS.h>
+#include <GCS_MAVLink/GCS_config.h>
+#if HAL_GCS_ENABLED
+#include <GCS_MAVLink/GCS_MAVLink.h>
 #endif
 
 #ifndef AP_CHECK_FIRMWARE_ENABLED
diff --git a/libraries/AP_CheckFirmware/AP_CheckFirmware_secure_command.cpp b/libraries/AP_CheckFirmware/AP_CheckFirmware_secure_command.cpp
index d6578d8c5a98c..0357c42e728d5 100644
--- a/libraries/AP_CheckFirmware/AP_CheckFirmware_secure_command.cpp
+++ b/libraries/AP_CheckFirmware/AP_CheckFirmware_secure_command.cpp
@@ -7,7 +7,11 @@
 #if AP_CHECK_FIRMWARE_ENABLED && AP_SIGNED_FIRMWARE && !defined(HAL_BOOTLOADER_BUILD)
 
 #include "monocypher.h"
-#include <AP_Math/crc.h>
+#include <AP_Math/AP_Math.h>
+
+#if HAL_GCS_ENABLED
+#include <GCS_MAVLink/GCS.h>
+#endif
 
 extern const AP_HAL::HAL &hal;
 
diff --git a/libraries/AP_EFI/AP_EFI_NWPMU.cpp b/libraries/AP_EFI/AP_EFI_NWPMU.cpp
index 3c0316772c5d2..44c8c947ec832 100644
--- a/libraries/AP_EFI/AP_EFI_NWPMU.cpp
+++ b/libraries/AP_EFI/AP_EFI_NWPMU.cpp
@@ -18,6 +18,7 @@
 #include <AP_Common/AP_Common.h>
 #include <AP_HAL/utility/sparse-endian.h>
 #include <AP_Math/AP_Math.h>
+#include <GCS_MAVLink/GCS.h>
 
 #include "AP_EFI_NWPMU.h"
 
diff --git a/libraries/AP_Frsky_Telem/AP_Frsky_MAVliteMsgHandler.cpp b/libraries/AP_Frsky_Telem/AP_Frsky_MAVliteMsgHandler.cpp
index 9952f6c6aedd5..75daa6c4c2e4c 100644
--- a/libraries/AP_Frsky_Telem/AP_Frsky_MAVliteMsgHandler.cpp
+++ b/libraries/AP_Frsky_Telem/AP_Frsky_MAVliteMsgHandler.cpp
@@ -2,6 +2,7 @@
 
 #include <AC_Fence/AC_Fence.h>
 #include <AP_Vehicle/AP_Vehicle.h>
+#include <GCS_MAVLink/GCS.h>
 
 extern const AP_HAL::HAL& hal;
 
@@ -291,4 +292,4 @@ bool AP_Frsky_MAVliteMsgHandler::send_message(AP_Frsky_MAVlite_Message &txmsg)
 {
     return _send_fn(txmsg);
 }
-#endif
\ No newline at end of file
+#endif
diff --git a/libraries/AP_Generator/AP_Generator_RichenPower.cpp b/libraries/AP_Generator/AP_Generator_RichenPower.cpp
index 99c18f7c71431..16b8fbcce0d8d 100644
--- a/libraries/AP_Generator/AP_Generator_RichenPower.cpp
+++ b/libraries/AP_Generator/AP_Generator_RichenPower.cpp
@@ -20,6 +20,7 @@
 #include <AP_Logger/AP_Logger.h>
 #include <AP_SerialManager/AP_SerialManager.h>
 #include <AP_Vehicle/AP_Vehicle.h>
+#include <GCS_MAVLink/GCS.h>
 
 #include <AP_HAL/utility/sparse-endian.h>
 
diff --git a/libraries/AP_HAL_ChibiOS/Util.h b/libraries/AP_HAL_ChibiOS/Util.h
index 53d5880bd5bdb..dcc5fd3dab4c7 100644
--- a/libraries/AP_HAL_ChibiOS/Util.h
+++ b/libraries/AP_HAL_ChibiOS/Util.h
@@ -20,9 +20,6 @@
 #include "AP_HAL_ChibiOS_Namespace.h"
 #include "AP_HAL_ChibiOS.h"
 #include <ch.h>
-#if !defined(HAL_BOOTLOADER_BUILD)
-#include <GCS_MAVLink/GCS.h>
-#endif
 
 class ExpandingString;
 
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
index 8bc45c77e6ee7..7703d6079a3c1 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
+++ b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
@@ -2960,6 +2960,11 @@ def add_bootloader_defaults(f):
 #define HAL_GYROFFT_ENABLED 0
 #endif
 
+// bootloaders don't talk to the GCS:
+#ifndef HAL_GCS_ENABLED
+#define HAL_GCS_ENABLED 0
+#endif
+
 #define HAL_MAX_CAN_PROTOCOL_DRIVERS 0
 ''')
 
diff --git a/libraries/AP_Motors/AP_MotorsMatrix_6DoF_Scripting.cpp b/libraries/AP_Motors/AP_MotorsMatrix_6DoF_Scripting.cpp
index 68837569d5564..386c2e83c0651 100644
--- a/libraries/AP_Motors/AP_MotorsMatrix_6DoF_Scripting.cpp
+++ b/libraries/AP_Motors/AP_MotorsMatrix_6DoF_Scripting.cpp
@@ -19,6 +19,7 @@
 #include "AP_MotorsMatrix_6DoF_Scripting.h"
 #include <GCS_MAVLink/GCS.h>
 #include <SRV_Channel/SRV_Channel.h>
+#include <GCS_MAVLink/GCS.h>
 
 extern const AP_HAL::HAL& hal;
 
diff --git a/libraries/AP_OSD/AP_OSD.cpp b/libraries/AP_OSD/AP_OSD.cpp
index 9a4003aae96d9..6b44ea58869bc 100644
--- a/libraries/AP_OSD/AP_OSD.cpp
+++ b/libraries/AP_OSD/AP_OSD.cpp
@@ -36,6 +36,7 @@
 #include <AP_Notify/AP_Notify.h>
 #include <AP_Terrain/AP_Terrain.h>
 #include <AP_RSSI/AP_RSSI.h>
+#include <GCS_MAVLink/GCS.h>
 
 // macro for easy use of var_info2
 #define AP_SUBGROUPINFO2(element, name, idx, thisclazz, elclazz) { AP_PARAM_GROUP, idx, name, AP_VAROFFSET(thisclazz, element), { group_info : elclazz::var_info2 }, AP_PARAM_FLAG_NESTED_OFFSET }
diff --git a/libraries/AP_OSD/AP_OSD.h b/libraries/AP_OSD/AP_OSD.h
index 82ac968161072..25583292fee26 100644
--- a/libraries/AP_OSD/AP_OSD.h
+++ b/libraries/AP_OSD/AP_OSD.h
@@ -22,11 +22,13 @@
 #include <AP_Math/AP_Math.h>
 #include <AP_ESC_Telem/AP_ESC_Telem.h>
 #include <RC_Channel/RC_Channel.h>
-#include <GCS_MAVLink/GCS.h>
+#include <GCS_MAVLink/GCS_config.h>
 #include <AP_OLC/AP_OLC.h>
 #include <AP_MSP/msp.h>
 #include <AP_Baro/AP_Baro.h>
+#if HAL_GCS_ENABLED
 #include <GCS_MAVLink/GCS_MAVLink.h>
+#endif
 #include <AC_Fence/AC_Fence_config.h>
 
 #ifndef OSD_ENABLED
@@ -349,8 +351,10 @@ class AP_OSD_ParamSetting : public AP_OSD_Setting
 
     static const ParamMetadata _param_metadata[];
 
+#if HAL_GCS_ENABLED
     AP_OSD_ParamSetting(uint8_t param_number, bool enabled, uint8_t x, uint8_t y, int16_t key, int8_t idx, int32_t group,
         int8_t type = OSD_PARAM_NONE, float min = 0.0f, float max = 1.0f, float incr = 0.001f);
+#endif
     AP_OSD_ParamSetting(uint8_t param_number);
     AP_OSD_ParamSetting(const Initializer& initializer);
 
@@ -408,8 +412,8 @@ class AP_OSD_ParamScreen : public AP_OSD_AbstractScreen
     void draw(void) override;
 #endif
 #if HAL_GCS_ENABLED
-    void handle_write_msg(const mavlink_osd_param_config_t& packet, const GCS_MAVLINK& link);
-    void handle_read_msg(const mavlink_osd_param_show_config_t& packet, const GCS_MAVLINK& link);
+    void handle_write_msg(const mavlink_osd_param_config_t& packet, const class GCS_MAVLINK& link);
+    void handle_read_msg(const mavlink_osd_param_show_config_t& packet, const class GCS_MAVLINK& link);
 #endif
     // get a setting and associated metadata
     AP_OSD_ParamSetting* get_setting(uint8_t param_idx);
@@ -593,7 +597,7 @@ class AP_OSD
 #endif
     // handle OSD parameter configuration
 #if HAL_GCS_ENABLED
-    void handle_msg(const mavlink_message_t &msg, const GCS_MAVLINK& link);
+    void handle_msg(const mavlink_message_t &msg, const class GCS_MAVLINK& link);
 #endif
 
     // allow threads to lock against OSD update
diff --git a/libraries/AP_OSD/AP_OSD_Backend.cpp b/libraries/AP_OSD/AP_OSD_Backend.cpp
index 705a468c9d583..df1242968e293 100644
--- a/libraries/AP_OSD/AP_OSD_Backend.cpp
+++ b/libraries/AP_OSD/AP_OSD_Backend.cpp
@@ -16,6 +16,7 @@
 
 #include <AP_OSD/AP_OSD_Backend.h>
 #include <AP_HAL/Util.h>
+#include <GCS_MAVLink/GCS.h>
 #include <ctype.h>
 
 extern const AP_HAL::HAL& hal;
diff --git a/libraries/AP_OSD/AP_OSD_MSP_DisplayPort.cpp b/libraries/AP_OSD/AP_OSD_MSP_DisplayPort.cpp
index 2336e8327795c..8a9191e8d8fa6 100644
--- a/libraries/AP_OSD/AP_OSD_MSP_DisplayPort.cpp
+++ b/libraries/AP_OSD/AP_OSD_MSP_DisplayPort.cpp
@@ -22,6 +22,8 @@
 
 #if HAL_WITH_MSP_DISPLAYPORT
 
+#include <GCS_MAVLink/GCS.h>
+
 static const struct AP_Param::defaults_table_struct defaults_table[] = {
     /*
     { "PARAM_NAME",       value_float }
@@ -131,4 +133,4 @@ AP_OSD_Backend *AP_OSD_MSP_DisplayPort::probe(AP_OSD &osd)
     }
     return backend;
 }
-#endif
\ No newline at end of file
+#endif
diff --git a/libraries/AP_OSD/AP_OSD_ParamScreen.cpp b/libraries/AP_OSD/AP_OSD_ParamScreen.cpp
index b626296d0d8d4..8b9b5b4934bd3 100644
--- a/libraries/AP_OSD/AP_OSD_ParamScreen.cpp
+++ b/libraries/AP_OSD/AP_OSD_ParamScreen.cpp
@@ -30,6 +30,7 @@
 #include <AP_Vehicle/AP_Vehicle_Type.h>
 #include <AP_Arming/AP_Arming.h>
 #include <AP_Vehicle/AP_Vehicle_Type.h>
+#include <GCS_MAVLink/GCS.h>
 
 extern const AP_HAL::HAL& hal;
 
diff --git a/libraries/AP_OSD/AP_OSD_ParamSetting.cpp b/libraries/AP_OSD/AP_OSD_ParamSetting.cpp
index a57aca80878d7..6e012fbcc7b02 100644
--- a/libraries/AP_OSD/AP_OSD_ParamSetting.cpp
+++ b/libraries/AP_OSD/AP_OSD_ParamSetting.cpp
@@ -23,6 +23,7 @@
 
 #include "AP_OSD.h"
 #include <AP_Vehicle/AP_Vehicle_Type.h>
+#include <GCS_MAVLink/GCS.h>
 #include <SRV_Channel/SRV_Channel.h>
 #include <ctype.h>
 
diff --git a/libraries/AP_OpenDroneID/AP_OpenDroneID.cpp b/libraries/AP_OpenDroneID/AP_OpenDroneID.cpp
index 24a4ceab985ce..065eac33f0c8d 100644
--- a/libraries/AP_OpenDroneID/AP_OpenDroneID.cpp
+++ b/libraries/AP_OpenDroneID/AP_OpenDroneID.cpp
@@ -33,8 +33,6 @@
 
 #include <AP_HAL/AP_HAL.h>
 #include <GCS_MAVLink/GCS.h>
-#include <GCS_MAVLink/GCS_MAVLink.h>
-#include <GCS_MAVLink/GCS.h>
 #include <AP_GPS/AP_GPS.h>
 #include <AP_Baro/AP_Baro.h>
 #include <AP_AHRS/AP_AHRS.h>
diff --git a/libraries/AP_OpenDroneID/AP_OpenDroneID_DroneCAN.cpp b/libraries/AP_OpenDroneID/AP_OpenDroneID_DroneCAN.cpp
index a40f098248993..bd7a1df8647cf 100644
--- a/libraries/AP_OpenDroneID/AP_OpenDroneID_DroneCAN.cpp
+++ b/libraries/AP_OpenDroneID/AP_OpenDroneID_DroneCAN.cpp
@@ -30,7 +30,7 @@
 #include <dronecan/remoteid/System.hpp>
 #include <dronecan/remoteid/ArmStatus.hpp>
 
-#include <GCS_MAVLink/GCS_MAVLink.h>
+#include <GCS_MAVLink/GCS.h>
 
 static uavcan::Publisher<dronecan::remoteid::Location>* dc_location[HAL_MAX_CAN_PROTOCOL_DRIVERS];
 static uavcan::Publisher<dronecan::remoteid::BasicID>* dc_basic_id[HAL_MAX_CAN_PROTOCOL_DRIVERS];
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_UAVCAN.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_UAVCAN.cpp
index bf6f4e857d83e..cba78545cbb2d 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_UAVCAN.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_UAVCAN.cpp
@@ -5,6 +5,7 @@
 #include <AP_HAL/AP_HAL.h>
 #include <AP_CANManager/AP_CANManager.h>
 #include <AP_UAVCAN/AP_UAVCAN.h>
+#include <GCS_MAVLink/GCS.h>
 
 #include <uavcan/equipment/range_sensor/Measurement.hpp>
 
diff --git a/libraries/AP_Vehicle/AP_Vehicle.cpp b/libraries/AP_Vehicle/AP_Vehicle.cpp
index 294655d518afe..2d4016c0ae4e5 100644
--- a/libraries/AP_Vehicle/AP_Vehicle.cpp
+++ b/libraries/AP_Vehicle/AP_Vehicle.cpp
@@ -12,6 +12,7 @@
 #include <AP_Motors/AP_Motors.h>
 #include <AR_Motors/AP_MotorsUGV.h>
 #include <AP_CheckFirmware/AP_CheckFirmware.h>
+#include <GCS_MAVLink/GCS.h>
 #if CONFIG_HAL_BOARD == HAL_BOARD_CHIBIOS
 #include <AP_HAL_ChibiOS/sdcard.h>
 #include <AP_HAL_ChibiOS/hwdef/common/stm32_util.h>