diff --git a/comms/rubygem-serialport/Makefile b/comms/rubygem-serialport/Makefile
index d0a9e5a8591b..6ccbf07d725d 100644
--- a/comms/rubygem-serialport/Makefile
+++ b/comms/rubygem-serialport/Makefile
@@ -1,15 +1,23 @@
 PORTNAME=	serialport
 DISTVERSION=	1.3.2
 CATEGORIES=	comms rubygems
 MASTER_SITES=	RG
 
 MAINTAINER=	tj+freebsd_ports@a13.fr
 COMMENT=	Library for using RS-232 serial ports
 WWW=		https://rubygems.org/gems/serialport
 
 LICENSE=	GPLv2
 
 USES=		gem shebangfix
 SHEBANG_FILES=	test/set_readtimeout.rb
 
+.include <bsd.port.options.mk>
+
+post-patch:
+.if ${OPSYS} == FreeBSD && ( ${OSVERSION} >= 1400079 || ( ${OSVERSION} >= 1302505 && ${OSVERSION} < 1400000 ))
+	@${REINPLACE_CMD} -e 's|-DOS_\#{os.upcase}|-DOS_\#{os.upcase} -Wno-error=int-conversion|g' \
+		${WRKSRC}/ext/native/extconf.rb
+.endif
+
 .include <bsd.port.mk>