diff --git a/lang/csharp-mode.el/Makefile b/lang/csharp-mode.el/Makefile
index 8ebc6e178e69..97801c2af5bf 100644
--- a/lang/csharp-mode.el/Makefile
+++ b/lang/csharp-mode.el/Makefile
@@ -1,28 +1,31 @@
 PORTNAME=	csharp-mode.el
 PORTVERSION=	2.0.0
 PORTREVISION=	1
 CATEGORIES=	lang elisp
 
 MAINTAINER=	ports@FreeBSD.org
 COMMENT=	Emacs major mode for editing C\# source code
 WWW=		https://github.com/josteink/csharp-mode
 
 LICENSE=	GPLv2
 
+DEPRECATED=	No longer maintained upstream as a standalone package. This mode is part of Emacs core since Emacs 29
+EXPIRATION_DATE=2026-06-30
+
 USES=		emacs
 USE_GITHUB=	yes
 GH_ACCOUNT=	josteink
 GH_PROJECT=	csharp-mode
 
 CONFLICTS_INSTALL=	csharp-mode.el-emacs_*
 
 NO_ARCH=	yes
 NO_BUILD=	yes
 
 PLIST_FILES=	${EMACS_SITE_LISPDIR}/csharp-mode.el
 
 do-install:
 	${INSTALL_DATA} ${WRKSRC}/csharp-mode.el \
 		${STAGEDIR}${PREFIX}/${EMACS_SITE_LISPDIR}
 
 .include <bsd.port.mk>