diff --git a/share/mk/Makefile b/share/mk/Makefile
index bfc3102e30c3..e63005cd382d 100644
--- a/share/mk/Makefile
+++ b/share/mk/Makefile
@@ -5,7 +5,7 @@ FILES=	bsd.README
 FILES+=	bsd.cpu.mk bsd.dep.mk bsd.doc.mk bsd.docb.mk bsd.info.mk bsd.kern.mk bsd.kmod.mk
 FILES+=	bsd.lib.mk bsd.libnames.mk bsd.man.mk bsd.obj.mk bsd.own.mk
 FILES+=	bsd.port.mk bsd.port.post.mk  bsd.port.pre.mk bsd.port.subdir.mk
-FILES+=	bsd.prog.mk bsd.sgml.mk bsd.subdir.mk
+FILES+=	bsd.prog.mk bsd.sgml.mk bsd.subdir.mk bsd.sys.mk
 FILES+=	sys.mk
 NOOBJ=	noobj
 
diff --git a/share/mk/bsd.kmod.mk b/share/mk/bsd.kmod.mk
index 73f9c14cf07c..586369f97ddc 100644
--- a/share/mk/bsd.kmod.mk
+++ b/share/mk/bsd.kmod.mk
@@ -11,3 +11,5 @@ SYSDIR=	${_dir}
 .endif
 
 .include "${SYSDIR}/conf/kmod.mk"
+
+.include <bsd.sys.mk>
diff --git a/share/mk/bsd.lib.mk b/share/mk/bsd.lib.mk
index 96470ea19337..104cdc96849e 100644
--- a/share/mk/bsd.lib.mk
+++ b/share/mk/bsd.lib.mk
@@ -375,3 +375,5 @@ ${OBJS} ${STATICOBJS} ${POBJS} ${SOBJS}: ${SRCS:M*.h}
 .endif
 
 .include <bsd.obj.mk>
+
+.include <bsd.sys.mk>
diff --git a/share/mk/bsd.prog.mk b/share/mk/bsd.prog.mk
index 3c772989d719..646cf1214a56 100644
--- a/share/mk/bsd.prog.mk
+++ b/share/mk/bsd.prog.mk
@@ -222,3 +222,5 @@ ${OBJS}: ${SRCS:M*.h}
 .endif
 
 .include <bsd.obj.mk>
+
+.include <bsd.sys.mk>
diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
new file mode 100644
index 000000000000..efb69a9c97b4
--- /dev/null
+++ b/share/mk/bsd.sys.mk
@@ -0,0 +1,37 @@
+# $FreeBSD$
+#
+# This file contains common settings used for building FreeBSD
+# sources.
+
+# Enable various levels of compiler warning checks.  These may be
+# overridden (e.g. if using a non-gcc compiler) by defining NO_WARNS.
+
+.if !defined(NO_WARNS)
+. if defined(WARNS)
+.  if ${WARNS} > 0
+CFLAGS		+=	-W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith
+# XXX Delete -Wuninitialized by default for now -- the compiler doesn't
+# XXX always get it right.
+CFLAGS		+=	-Wno-uninitialized
+.  endif
+.  if ${WARNS} > 1
+CFLAGS		+=	-Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow
+.  endif
+. endif
+
+. if defined(FORMAT_AUDIT)
+WFORMAT		=	1
+. endif
+. if defined(WFORMAT)
+.  if ${WFORMAT} > 0
+CFLAGS		+=	-Wnon-const-format -Wno-format-extra-args
+.  endif
+. endif
+
+. if !defined(NO_WERROR)
+CFLAGS		+=	-Werror
+. endif
+.endif
+
+# Allow user-specified additional warning flags
+CFLAGS		+=	${CWARNFLAGS}