diff --git a/Makefile b/Makefile
index 3a16d26222d..fa6bac587af 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-SYSDIR?=/usr/src/sys
+SYSDIR?=${SRCTOP}/sys
 .include "${SYSDIR}/conf/kern.opts.mk"
 
 _VALID_KMODS=	dmabuf ttm drm dummygfx i915 amd radeon linuxkpi_video