diff --git a/libraries/AP_HAL/AP_HAL_Boards.h b/libraries/AP_HAL/AP_HAL_Boards.h
index ddfc1e8141..8dd860f754 100644
--- a/libraries/AP_HAL/AP_HAL_Boards.h
+++ b/libraries/AP_HAL/AP_HAL_Boards.h
@@ -40,6 +40,7 @@
 /* HAL PX4 sub-types, starting at 2000 */
 #define HAL_BOARD_SUBTYPE_PX4_V1           2000
 #define HAL_BOARD_SUBTYPE_PX4_V2           2001
+#define HAL_BOARD_SUBTYPE_PX4_V4           2002
 
 /* HAL VRBRAIN sub-types, starting at 4000 */
 #define HAL_BOARD_SUBTYPE_VRBRAIN_V45      4000
diff --git a/libraries/AP_HAL/board/px4.h b/libraries/AP_HAL/board/px4.h
index b81e0ecfdf..abd6774a2c 100644
--- a/libraries/AP_HAL/board/px4.h
+++ b/libraries/AP_HAL/board/px4.h
@@ -14,11 +14,16 @@
 #ifdef CONFIG_ARCH_BOARD_PX4FMU_V1
 #define CONFIG_HAL_BOARD_SUBTYPE HAL_BOARD_SUBTYPE_PX4_V1
 #define HAL_STORAGE_SIZE            8192
-#else
+#elif defined(CONFIG_ARCH_BOARD_PX4FMU_V2)
 #define CONFIG_HAL_BOARD_SUBTYPE HAL_BOARD_SUBTYPE_PX4_V2
 #define HAL_STORAGE_SIZE            16384
 #define HAL_HAVE_IMU_HEATER         1 // for Pixhawk2
 #define HAL_IMU_TEMP_DEFAULT       -1 // disabled
+#elif defined(CONFIG_ARCH_BOARD_PX4FMU_V4)
+#define CONFIG_HAL_BOARD_SUBTYPE HAL_BOARD_SUBTYPE_PX4_V4
+#define HAL_STORAGE_SIZE            16384
+#else
+#error "Unknown PX4 board type"
 #endif
 
 #define HAL_GPIO_A_LED_PIN        27