Index: Mk/Uses/kmod.mk
===================================================================
--- Mk/Uses/kmod.mk	(revision 502264)
+++ Mk/Uses/kmod.mk	(working copy)
@@ -25,6 +25,12 @@
 IGNORE=	requires kernel source files in ${SRC_BASE}
 .endif
 
+.if exists(${SRC_BASE}/sys/sys/param.h)
+SRC_BASE_VERSION!=	${AWK} '/^\#define[[:blank:]]__FreeBSD_version/ {print $$3}' < ${SRC_BASE}/sys/sys/param.h
+.else
+.error Unable to determine OS version.  Either define OSVERSION, install ${SRC_BASE}/sys/param.h.
+.endif
+
 CATEGORIES+=	kld
 
 SSP_UNSAFE=	kernel module supports SSP natively