diff --git a/devel/envsubst/Makefile b/devel/envsubst/Makefile
index b5a0544731f9..a88fcb0bfaf2 100644
--- a/devel/envsubst/Makefile
+++ b/devel/envsubst/Makefile
@@ -1,22 +1,23 @@
 PORTNAME=	envsubst
 PORTVERSION=	0.1
 
 CATEGORIES=	devel
 MASTER_SITES=	https://distfiles.dereferenced.org/envsubst/
 
 MAINTAINER=	bapt@FreeBSD.org
 COMMENT=	Perform variable substitutions on input
 
 LICENSE=	ISCL
 
 USES=		tar:xz
+USE_CSTD=	c99
 
 ALL_TARGET=	${PORTNAME}
 
 PLIST_FILES=	bin/isc-${PORTNAME}
 
 post-install:
 	${MV} ${STAGEDIR}${PREFIX}/bin/${PORTNAME} ${STAGEDIR}${PREFIX}/bin/isc-${PORTNAME}
 	${STRIP_CMD} ${STAGEDIR}${PREFIX}/bin/isc-${PORTNAME}
 
 .include <bsd.port.mk>