diff --git a/devel/isl/Makefile b/devel/isl/Makefile
--- a/devel/isl/Makefile
+++ b/devel/isl/Makefile
@@ -3,7 +3,7 @@
 PORTNAME=	isl
 PORTVERSION=	0.24
 CATEGORIES=	devel math
-MASTER_SITES=	http://isl.gforge.inria.fr/ GENTOO
+MASTER_SITES=	SOURCEFORGE/libisl
 
 MAINTAINER=	ports@FreeBSD.org
 COMMENT=	Integer Set Library
@@ -14,9 +14,17 @@
 LIB_DEPENDS=	libgmp.so:math/gmp
 
 USES=		libtool pkgconfig tar:xz
-CONFIGURE_ARGS=	--with-gmp-prefix=${LOCALBASE}
+USE_LDCONFIG=	yes
 GNU_CONFIGURE=	yes
+
 INSTALL_TARGET=	install-strip
-USE_LDCONFIG=	yes
+TEST_TARGET=	check
+
+CONFIGURE_ARGS=	--with-gmp-prefix=${LOCALBASE}
+
+OPTIONS_DEFINE=	OPTIMIZED_CFLAGS
+OPTIONS_DEFAULT=OPTIMIZED_CFLAGS
+
+OPTIMIZED_CFLAGS_CFLAGS=	-O3
 
 .include <bsd.port.mk>
diff --git a/devel/isl/files/patch-configure b/devel/isl/files/patch-configure
new file mode 100644
--- /dev/null
+++ b/devel/isl/files/patch-configure
@@ -0,0 +1,11 @@
+--- configure.orig	2021-10-14 09:28:15 UTC
++++ configure
+@@ -6984,7 +6984,7 @@ fi
+ 	echo "* (otherwise, a default of CFLAGS=-O3 will be used)    *"
+ 	echo "********************************************************"
+ 	echo ""
+-        CFLAGS="-O3"
++        CFLAGS="$ac_cv_env_CFLAGS_value"
+   fi
+ 
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts $CFLAGS" >&5
diff --git a/devel/isl/pkg-descr b/devel/isl/pkg-descr
--- a/devel/isl/pkg-descr
+++ b/devel/isl/pkg-descr
@@ -7,4 +7,4 @@
 basis reduction, transitive closures on maps (which may encode infinite
 graphs), dependence analysis and bounds on piecewise step-polynomials.
 
-WWW: http://isl.gforge.inria.fr/
+WWW: https://libisl.sourceforge.io/