diff --git a/mail/milter-manager/Makefile b/mail/milter-manager/Makefile
index 788173c7f8dd..19fc2fce4452 100644
--- a/mail/milter-manager/Makefile
+++ b/mail/milter-manager/Makefile
@@ -1,47 +1,48 @@
 # Created by: Hirohisa Yamaguchi <umq@ueo.co.jp>
 
 PORTNAME=	milter-manager
 DISTVERSION=	2.1.6
 CATEGORIES=	mail ruby
 MASTER_SITES=	https://github.com/${PORTNAME}/${PORTNAME}/releases/download/${DISTVERSION}/
 
 MAINTAINER=	ports@FreeBSD.org
 COMMENT=	Super milter that can invoke several milters selectively
 
 LICENSE=	AGPLv3 GFDL GPLv3 LGPL3
 LICENSE_COMB=	multi
 
 BUILD_DEPENDS=	rubygem-gio2>0:devel/rubygem-gio2
 LIB_DEPENDS=	libev.so:devel/libev
 RUN_DEPENDS=	rubygem-gio2>0:devel/rubygem-gio2
 
 USES=		compiler:c++11-lang gettext gmake gnome libtool pathfix \
 		pkgconfig
 USE_GNOME=	glib20 intltool
 USE_LDCONFIG=	yes
 USE_RC_SUBR=	milter-manager
 USE_RUBY=	yes
 
 GNU_CONFIGURE=	yes
 CONFIGURE_ARGS=	--with-html-dir=${DOCSDIR} \
 		--with-libev \
 		--with-package-platform=freebsd
 
 INSTALL_TARGET=	install-strip
 
+CFLAGS+=	-fdeclspec
 CPPFLAGS+=	-I${LOCALBASE}/include
 LIBS+=		-L${LOCALBASE}/lib
 
 PORTDOCS=	*
 PORTEXAMPLES=	*
 
 OPTIONS_DEFINE=	DOCS EXAMPLES
 
 post-patch:
 	@${FIND} ${WRKSRC} -type f -name Makefile.in -exec \
 	${REINPLACE_CMD} -e "s#\$$(datadir)/@PACKAGE@#${DATADIR}#" \
 			 -e "s#\$$(datarootdir)/\$$(PACKAGE)#${DATADIR}#" {} +
 	@${REINPLACE_CMD} -e "s#\\\\\$$(pkgdatadir)/sample#${EXAMPLESDIR}#" ${WRKSRC}/configure
 	@${RM} -r ${WRKSRC}/binding/ruby/glib-2.2.5
 
 .include <bsd.port.mk>