Index: head/cad/iverilog/Makefile
===================================================================
--- head/cad/iverilog/Makefile	(revision 398889)
+++ head/cad/iverilog/Makefile	(revision 398890)
@@ -1,20 +1,27 @@
 # Created by: Ying-Chieh Liao <ijliao@FreeBSD.org>
 # $FreeBSD$
 
 PORTNAME=	iverilog
 PORTVERSION=	10.0
 CATEGORIES=	cad
 MASTER_SITES=	ftp://icarus.com/pub/eda/verilog/v${PORTVERSION:C,\.[0-9]$,,}/
 DISTNAME=	verilog-${PORTVERSION}
 
 MAINTAINER=	zeising@FreeBSD.org
 COMMENT=	Verilog simulation and synthesis tool
 
 LICENSE=	GPLv2
 
 GNU_CONFIGURE=	yes
 USES=		bison gmake
 
+.include <bsd.port.options.mk>
+
+.if ${OSVERSION} < 1000033
+BUILD_DEPENDS+=	flex>=0:${PORTSDIR}/textproc/flex
+CONFIGURE_ENV+=	ac_cv_prog_LEX="${LOCALBASE}/bin/flex"
+.endif
+
 CONFIGURE_ARGS=	--disable-suffix
 
 .include <bsd.port.mk>