diff -Nurp VirtualBox-5.2.2.orig/src/VBox/Additions/common/VBoxGuest/lib/Makefile.kmk VirtualBox-5.2.2/src/VBox/Additions/common/VBoxGuest/lib/Makefile.kmk
--- VirtualBox-5.2.2.orig/src/VBox/Additions/common/VBoxGuest/lib/Makefile.kmk	2017-11-23 11:15:53.000000000 +0200
+++ VirtualBox-5.2.2/src/VBox/Additions/common/VBoxGuest/lib/Makefile.kmk	2017-11-25 16:03:29.018044333 +0200
@@ -40,9 +40,11 @@ LIBRARIES += \
 	VBoxGuestR3LibShared
 ifndef VBOX_ONLY_VALIDATIONKIT
  if1of ($(KBUILD_TARGET), freebsd linux netbsd openbsd)
+ ifndef VBOX_USE_SYSTEM_XORG_HEADERS
   LIBRARIES += \
   	VBoxGuestR3LibXFree86
  endif
+ endif
  if1of ($(KBUILD_TARGET), freebsd linux netbsd openbsd solaris)
   LIBRARIES += \
   	VBoxGuestR3LibXOrg