diff --git a/textproc/flex/Makefile b/textproc/flex/Makefile
index 0d39fb3e4e4e..a4db6e07401b 100644
--- a/textproc/flex/Makefile
+++ b/textproc/flex/Makefile
@@ -1,42 +1,48 @@
 PORTNAME=	flex
 PORTVERSION=	2.6.4
 PORTREVISION=	2
 CATEGORIES=	textproc devel
 MASTER_SITES=	https://github.com/westes/flex/releases/download/v${PORTVERSION}/
 
 MAINTAINER=	mandree@FreeBSD.org
 COMMENT=	Fast lexical analyzer generator
 
 LICENSE=	BSD3CLAUSE
 LICENSE_FILE=	${WRKSRC}/COPYING
 
 BUILD_DEPENDS=	help2man:misc/help2man
 
 USES=		bison:alias gmake libtool makeinfo
 GNU_CONFIGURE=	yes
 # install flex header to its own dir to avoid conflict with system flex.
 CONFIGURE_ARGS=	--includedir=${PREFIX}/include/flex --disable-shared
-CONFIGURE_ENV=	MAKEINFO="${MAKEINFO} --no-split"
+CONFIGURE_ENV=	MAKEINFO="${MAKEINFO} --no-split" \
+		CC_FOR_BUILD="${CC}" \
+                CFLAGS_FOR_BUILD="${CFLAGS}" \
+                CPPFLAGS_FOR_BUILD="${CPPFLAGS}" \
+                CXX_FOR_BUILD="${CXX}" \
+                CXXFLAGS_FOR_BUILD="${CXXFLAGS}" \
+                LDFLAGS_FOR_BUILD="${LDFLAGS}"
 INSTALL_TARGET=	install-strip
 
 INFO=		flex
 PORTDOCS=	*
 PORTEXAMPLES=	*
 
 OPTIONS_DEFINE=	DOCS EXAMPLES NLS
 OPTIONS_SUB=	yes
 NLS_USES=	gettext iconv
 NLS_CONFIGURE_ENABLE=	nls
 
 post-patch:	.SILENT
 	${REINPLACE_CMD} -Ee 's/tests//' \
 		-e '/mode=compile ..CC/s/\\$$/-fPIC -DPIC &/' \
 		${WRKSRC}/Makefile.in
 	${RM} ${WRKSRC}/doc/*.info*
 
 post-install-EXAMPLES-on:
 	@${MKDIR} ${STAGEDIR}${EXAMPLESDIR}
 	${CP} -r ${WRKSRC}/examples/* ${STAGEDIR}${EXAMPLESDIR}/
 	${RM} ${STAGEDIR}${EXAMPLESDIR}/Makefile.am
 
 .include <bsd.port.mk>