diff --git a/lang/s9fes/Makefile b/lang/s9fes/Makefile
index f782a516e9bc..174d71c267c1 100644
--- a/lang/s9fes/Makefile
+++ b/lang/s9fes/Makefile
@@ -13,14 +13,14 @@ MASTER_SITES=	http://www.t3x.org/misc/
 MAINTAINER=	nmh@t3x.org
 COMMENT=	A portable Scheme interpreter with a Unix interface
 
+MAKE_ARGS=	CC=${CC} CFLAGS="${CFLAGS}" PREFIX=${PREFIX} LIBDIR=${DATADIR}
 WRKSRC=		${WRKDIR}/s9
 
 MAN1=		s9.1
 MANCOMPRESSED=	yes
-MAKE_JOBS_UNSAFE=	yes
 
 post-patch:
-	${REINPLACE_CMD} -e "s,PREFIX=.*,PREFIX=${PREFIX}," ${WRKSRC}/Makefile
-	${REINPLACE_CMD} -e "s,LIBDIR=.*,LIBDIR=${DATADIR}," ${WRKSRC}/Makefile
+# Fix parallel (-jX) build: add missing target prerequisite
+	@${REINPLACE_CMD} -e '/^arse-core.image/s,:,: s9,' ${WRKSRC}/Makefile
 
 .include <bsd.port.mk>