diff --git a/mk/px4_targets.mk b/mk/px4_targets.mk
index e7a64baae2..b255640de3 100644
--- a/mk/px4_targets.mk
+++ b/mk/px4_targets.mk
@@ -11,7 +11,7 @@ $(error ERROR: PX4_ROOT not set correctly - no nuttx directory found)
 endif
 
 PX4_CONFIG_FILE=$(MK_DIR)/PX4/config_px4fmu_APM.mk
-SKETCHFLAGS=$(SKETCHLIBINCLUDES) -I$(PWD) -DCONFIG_HAL_BOARD=HAL_BOARD_PX4 -DSKETCHNAME="\\\"$(SKETCH)\\\"" -DSKETCH_MAIN=ArduPilot_main
+SKETCHFLAGS=$(SKETCHLIBINCLUDES) -I$(PWD) -DARDUPILOT_BUILD -DCONFIG_HAL_BOARD=HAL_BOARD_PX4 -DSKETCHNAME="\\\"$(SKETCH)\\\"" -DSKETCH_MAIN=ArduPilot_main
 PX4_MAKE = make -C $(BUILDROOT) -f $(PX4_ROOT)/makefiles/firmware.mk CONFIG_FILE=$(PWD)/$(PX4_CONFIG_FILE) EXTRADEFINES="$(SKETCHFLAGS) "$(EXTRAFLAGS) APM_MODULE_DIR=$(BUILDROOT) SKETCHBOOK=$(SKETCHBOOK) PX4_ROOT=$(PX4_ROOT)
 
 $(BUILDROOT)/module.mk: