diff --git a/math/spot/Makefile b/math/spot/Makefile
index 49bab3f3215c..3a331ceb418d 100644
--- a/math/spot/Makefile
+++ b/math/spot/Makefile
@@ -1,29 +1,31 @@
 PORTNAME=	spot
 DISTVERSION=	2.10.5
 CATEGORIES=	math
 MASTER_SITES=	http://www.lrde.epita.fr/dload/${PORTNAME}/
 
 MAINTAINER=	yuri@FreeBSD.org
 COMMENT=	Library for omega automata manipulation and model checking
 
 LICENSE=	GPLv3
 LICENSE_FILE=	${WRKSRC}/COPYING
 
 USES=		charsetfix compiler:c++17-lang gmake libtool
 USE_LDCONFIG=	yes
 
 GNU_CONFIGURE=	yes
 CONFIGURE_ARGS=	--disable-python --disable-static
 
+CXXFLAGS+=	-Drestrict= # fix build problem on 13.0, 12.3 and earlier systems because clang-11 and earlier don't understand the restrict keyword
+
 INSTALL_TARGET=	install-strip
 
 OPTIONS_DEFINE=	DOCS
 
 PORTDOCS=	tl.pdf
 
 TEST_TARGET=	check
 
 post-install:
 	@${STRIP_CMD} ${STAGEDIR}${PREFIX}/lib/*.so
 
 .include <bsd.port.mk>