diff --git a/devel/isl/Makefile b/devel/isl/Makefile
index 54abca58a94d..fa5865e54a4b 100644
--- a/devel/isl/Makefile
+++ b/devel/isl/Makefile
@@ -1,22 +1,30 @@
 # Created by: Gea-Suan Lin <gslin@gslin.org>
 
 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
 
 LICENSE=	MIT
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
 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
index 000000000000..c8fd69bf9de6
--- /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
index d45dea5b4857..54aecf7d3203 100644
--- a/devel/isl/pkg-descr
+++ b/devel/isl/pkg-descr
@@ -1,10 +1,10 @@
 isl is a library for manipulating sets and relations of integer points
 bounded by linear constraints. Supported operations on sets include
 intersection, union, set difference, emptiness check, convex hull,
 (integer) affine hull, integer projection, computing the lexicographic
 minimum using parametric integer programming, coalescing and parametric
 vertex enumeration. It also includes an ILP solver based on generalized
 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/