diff --git a/tests/sys/netinet6/Makefile b/tests/sys/netinet6/Makefile
index 6af0d13c5f03..d06e8069a7fd 100644
--- a/tests/sys/netinet6/Makefile
+++ b/tests/sys/netinet6/Makefile
@@ -1,52 +1,55 @@
 
 PACKAGE=	tests
 
 TESTSDIR=	${TESTSBASE}/sys/netinet6
 FILESDIR=	${TESTSDIR}
 
 ATF_TESTS_PYTEST=	test_ip6_output.py
 ATF_TESTS_SH=		exthdr \
 			mld \
 			scapyi386 \
 			redirect \
 			divert \
 			forward6 \
 			output6 \
 			lpm6 \
 			fibs6 \
 			ndp \
-			proxy_ndp
+			proxy_ndp \
+			addr6
 
 TEST_METADATA.divert+=	execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets"
 TEST_METADATA.exthdr+=	execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets"
 TEST_METADATA.forward6+= execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets"
 TEST_METADATA.ndp+=	execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets"
 TEST_METADATA.output6+=	execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets" \
 			required_programs="python"
 TEST_METADATA.proxy_ndp+= execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets"
 TEST_METADATA.redirect+= execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets"
 TEST_METADATA.scapyi386+= execenv="jail"		\
 			execenv_jail_params="vnet allow.raw_sockets"
+TEST_METADATA.addr6+= execenv="jail"		\
+			execenv_jail_params="vnet allow.raw_sockets"
 
 ${PACKAGE}FILES+=	exthdr.py \
 			mld.py \
 			scapyi386.py \
 			ra.py \
 			redirect.py
 
 ${PACKAGE}FILESMODE_exthdr.py=	0555
 ${PACKAGE}FILESMODE_mld.py=	0555
 ${PACKAGE}FILESMODE_scapyi386.py=0555
 ${PACKAGE}FILESMODE_ra.py=0555
 ${PACKAGE}FILESMODE_redirect.py=0555
 
 TESTS_SUBDIRS+=	frag6
 
 .include <bsd.test.mk>
diff --git a/tests/sys/netinet6/addr6.sh b/tests/sys/netinet6/addr6.sh
new file mode 100755
index 000000000000..38e4bb152240
--- /dev/null
+++ b/tests/sys/netinet6/addr6.sh
@@ -0,0 +1,45 @@
+#!/usr/bin/env atf-sh
+#-
+# SPDX-License-Identifier: ISC
+#
+# Copyright (c) 2025 Lexi Winter.
+#
+# Permission to use, copy, modify, and distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+. $(atf_get_srcdir)/../common/vnet.subr
+
+atf_test_case "addr6_invalid_addr" "cleanup"
+addr6_invalid_addr_head()
+{
+	atf_set descr "adding an invalid IPv6 address returns an error"
+	atf_set require.user root
+}
+
+addr6_invalid_addr_body()
+{
+	vnet_init
+
+	ep=$(vnet_mkepair)
+	atf_check -s exit:0 ifconfig ${ep}a inet6 2001:db8::1/128
+	atf_check -s exit:1 -e ignore ifconfig ${ep}a inet6 2001:db8::1/127 alias
+}
+
+addr6_invalid_addr_cleanup()
+{
+	vnet_cleanup
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case "addr6_invalid_addr"
+}