Index: head/devel/mdb/Makefile
===================================================================
--- head/devel/mdb/Makefile	(revision 447183)
+++ head/devel/mdb/Makefile	(revision 447184)
@@ -1,36 +1,42 @@
 # $FreeBSD$
 
 PORTNAME=	mdb
 PORTVERSION=	0.1
 CATEGORIES=	devel
 
 MAINTAINER=	jhb@FreeBSD.org
 COMMENT=	Solaris Modular Debugger
 
 LICENSE=	CDDL
 
 USES=		uidfix
 
 USE_GITHUB=	yes
 GH_ACCOUNT=	bsdjhb
 GH_PROJECT=	illumos-gate
 GH_TAGNAME=	b8a73a7590
 
 ONLY_FOR_ARCHS=	amd64
 
 MAKE_ARGS=	WITH_CTF=yes
 MAKE_ARGS+=	BINDIR=${PREFIX}/bin
 MAKE_ARGS+=	LIBDIR=${PREFIX}/lib
 WRKSRC_SUBDIR=	freebsd/cddl/usr.bin/mdb
 CFLAGS+=	-DMDB_PREFIX=\\\"${PREFIX}\\\" -g
 
 .include <bsd.port.pre.mk>
 
+.if ${OSVERSION} < 1100021
+# This port uses CWARNFLAGS.clang to silence warnings which only works
+# in 11.0 and later.
+MAKE_ARGS+=	NO_WERROR=yes
+.endif
+
 .if !exists(${SRC_BASE}/cddl/compat) || !exists(${SRC_BASE}/sys/cddl/compat)
 IGNORE=		requires full source tree with CDDL sources
 .endif
 
 pre-install:
 	${MKDIR} ${STAGEDIR}${PREFIX}/lib/mdb/kvm/${MACHINE_ARCH}
 
 .include <bsd.port.post.mk>