diff --git a/devel/aws-c-io/Makefile b/devel/aws-c-io/Makefile
index 4c8d4a093e8d..613c1f4f178c 100644
--- a/devel/aws-c-io/Makefile
+++ b/devel/aws-c-io/Makefile
@@ -1,28 +1,31 @@
 PORTNAME=	aws-c-io
 DISTVERSIONPREFIX=	v
-DISTVERSION=	0.13.20
+DISTVERSION=	0.13.21
 CATEGORIES=	devel
 
 MAINTAINER=	eduardo@FreeBSD.org
 COMMENT=	Event driven framework for implementing application protocols
 WWW=		https://github.com/awslabs/aws-c-io
 
 LICENSE=	APACHE20
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
 LIB_DEPENDS=	libaws-c-cal.so:security/aws-c-cal \
 		libaws-c-common.so:devel/aws-c-common \
 		libs2n.so:security/s2n-tls
 
 USES=		cmake:testing compiler:c11 ssl
 
 USE_GITHUB=	yes
 GH_ACCOUNT=	awslabs
 
 USE_LDCONFIG=	yes
 
+# do-test: fails, "ld: error: lib/libaws-c-cal.so.1.0.0: undefined reference to aws_device_random_buffer_append [--no-allow-shlib-undefined]"
+# see also: https://github.com/awslabs/aws-c-io/issues/565
+
 CMAKE_ARGS+=	-DCMAKE_INSTALL_LIBDIR=${LOCALBASE}/lib
 CMAKE_ON=	BUILD_SHARED_LIBS
 CMAKE_OFF=	BUILD_TESTING
 
 .include <bsd.port.mk>
diff --git a/devel/aws-c-io/distinfo b/devel/aws-c-io/distinfo
index c20a5bbdd412..556e2007f6bb 100644
--- a/devel/aws-c-io/distinfo
+++ b/devel/aws-c-io/distinfo
@@ -1,3 +1,3 @@
-TIMESTAMP = 1681241434
-SHA256 (awslabs-aws-c-io-v0.13.20_GH0.tar.gz) = 0df70c9ad6022181d61bcf44a274dc1507f93a26b6c4cfc37f5cf2b59cfa7f3a
-SIZE (awslabs-aws-c-io-v0.13.20_GH0.tar.gz) = 646044
+TIMESTAMP = 1681718748
+SHA256 (awslabs-aws-c-io-v0.13.21_GH0.tar.gz) = f7811e2dc9ce2875410cf5eee45d1d4a3304d597a6df866384cbd98ed6341bd5
+SIZE (awslabs-aws-c-io-v0.13.21_GH0.tar.gz) = 647300