diff -urN a/src/VBox/HostDrivers/VBoxNetAdp/linux/Makefile b/src/VBox/HostDrivers/VBoxNetAdp/linux/Makefile
--- a/src/VBox/HostDrivers/VBoxNetAdp/linux/Makefile
+++ b/src/VBox/HostDrivers/VBoxNetAdp/linux/Makefile
@@ -58,7 +58,7 @@
 	RT_WITH_VBOX \
 	VBOX_WITH_HARDENING \
 	VBOX_WITH_64_BITS_GUESTS # <-- must be consistent with Config.kmk!
-VBOXMOD_CFLAGS = -include $(KBUILD_EXTMOD)/include/VBox/SUPDrvMangling.h -fno-pie -Wno-declaration-after-statement
+VBOXMOD_CFLAGS = -include $(VBOXNETADPT_DIR)include/VBox/SUPDrvMangling.h -fno-pie -Wno-declaration-after-statement
 
 include $(obj)/Makefile-footer.gmk