diff --git a/kmod/src/quorum.c b/kmod/src/quorum.c
index 9ef19276..08d5b9d3 100644
--- a/kmod/src/quorum.c
+++ b/kmod/src/quorum.c
@@ -1244,6 +1244,7 @@ static int verify_quorum_slots(struct super_block *sb, struct quorum_info *qinf,
 	struct sockaddr_in *other4;
 	struct sockaddr_in6 *sin6;
 	struct sockaddr_in6 *other6;
+	__le16 family = cpu_to_le16(SCOUTFS_AF_NONE);
 	int found = 0;
 	int ret;
 	int i;
@@ -1255,6 +1256,14 @@ static int verify_quorum_slots(struct super_block *sb, struct quorum_info *qinf,
 			continue;
 
 		if (quorum_slot_ipv4(qconf, i)) {
+			if (family == cpu_to_le16(SCOUTFS_AF_NONE)) {
+				family = cpu_to_le16(SCOUTFS_AF_IPV4);
+			} else if (family != cpu_to_le16(SCOUTFS_AF_IPV4)) {
+				scoutfs_err(sb, "quorum slot #%d is IPv4 but earlier slots are IPv6; mixed IPv4/IPv6 quorum is not supported",
+					    i);
+				return -EINVAL;
+			}
+
 			scoutfs_quorum_slot_sin(qconf, i, &sin);
 			sin4 = (struct sockaddr_in *)&sin;
 
@@ -1287,6 +1296,14 @@ static int verify_quorum_slots(struct super_block *sb, struct quorum_info *qinf,
 
 			found++;
 		} else if (quorum_slot_ipv6(qconf, i)) {
+			if (family == cpu_to_le16(SCOUTFS_AF_NONE)) {
+				family = cpu_to_le16(SCOUTFS_AF_IPV6);
+			} else if (family != cpu_to_le16(SCOUTFS_AF_IPV6)) {
+				scoutfs_err(sb, "quorum slot #%d is IPv6 but earlier slots are IPv4; mixed IPv4/IPv6 quorum is not supported",
+					    i);
+				return -EINVAL;
+			}
+
 			quorum_slot_sin(qconf, i, &sin);
 			sin6 = (struct sockaddr_in6 *)&sin;
 
diff --git a/tests/golden/basic-inetaddr b/tests/golden/basic-inetaddr
new file mode 100644
index 00000000..02d4d06b
--- /dev/null
+++ b/tests/golden/basic-inetaddr
@@ -0,0 +1,7 @@
+== mkfs rejects mixed v4/v6 quorum
+rc: 64
+== mkfs all-v4, mount three members, cross-mount signature visible
+== change-quorum-config rejects mixed v4/v6 quorum
+rc: 64
+== switch v4 -> v6, signature survives, cross-mount write again
+== switch v6 -> v4, signatures survive
diff --git a/tests/sequence b/tests/sequence
index 909e665a..671bcb80 100644
--- a/tests/sequence
+++ b/tests/sequence
@@ -1,6 +1,7 @@
 export-get-name-parent.sh
 basic-block-counts.sh
 basic-bad-mounts.sh
+basic-inetaddr.sh
 basic-posix-acl.sh
 basic-acl-consistency.sh
 inode-items-updated.sh
diff --git a/tests/tests/basic-inetaddr.sh b/tests/tests/basic-inetaddr.sh
new file mode 100644
index 00000000..67131896
--- /dev/null
+++ b/tests/tests/basic-inetaddr.sh
@@ -0,0 +1,78 @@
+#
+# Test that mixed ipv4/6 fails through mkfs/quorum change and that
+# users can migrate from ipv4 to v6 and back.
+#
+
+t_require_commands dmsetup blockdev cmp
+
+P0=$T_SCRATCH_PORT
+P1=$((T_SCRATCH_PORT + 1))
+P2=$((T_SCRATCH_PORT + 2))
+SIG=$T_TMP.sig
+seq 1 4096 > "$SIG"
+
+trap '
+	umount $T_TMPDIR/m0 $T_TMPDIR/m1 $T_TMPDIR/m2 2>/dev/null
+	dmsetup remove _bia_m0 _bia_m1 _bia_m2 _bia_d0 _bia_d1 _bia_d2 2>/dev/null
+' EXIT
+
+mkdir -p "$T_TMPDIR/m0" "$T_TMPDIR/m1" "$T_TMPDIR/m2"
+for nv in "m0 $T_EX_META_DEV" "m1 $T_EX_META_DEV" "m2 $T_EX_META_DEV" \
+	  "d0 $T_EX_DATA_DEV" "d1 $T_EX_DATA_DEV" "d2 $T_EX_DATA_DEV"; do
+	set -- $nv
+	t_quiet dmsetup create _bia_$1 --table "0 $(blockdev --getsz $2) linear $2 0"
+done
+
+mnt() {
+mount -t scoutfs \
+	-o metadev_path=/dev/mapper/_bia_m$1,quorum_slot_nr=$1 \
+	/dev/mapper/_bia_d$1 "$T_TMPDIR/m$1"
+}
+mount_all() {
+	mnt 0 &
+	mnt 1 &
+	mnt 2 &
+	wait
+}
+umount_all() {
+	umount $T_TMPDIR/m0 &
+	umount $T_TMPDIR/m1 &
+	umount $T_TMPDIR/m2 &
+	wait
+}
+verify() {
+	cmp -s "$SIG" "$T_TMPDIR/m0/sig" &&
+	cmp -s "$SIG" "$T_TMPDIR/m1/sig" &&
+	cmp -s "$SIG" "$T_TMPDIR/m2/sig" || t_fail "$1"
+}
+
+echo "== mkfs rejects mixed v4/v6 quorum"
+t_rc scoutfs mkfs -f -Q 0,127.0.0.1,$P0 -Q 1,::1,$P1 -Q 2,127.0.0.1,$P2 /dev/mapper/_bia_m0 /dev/mapper/_bia_d0
+
+echo "== mkfs all-v4, mount three members, cross-mount signature visible"
+t_quiet scoutfs mkfs -f -Q 0,127.0.0.1,$P0 -Q 1,127.0.0.1,$P1 -Q 2,127.0.0.1,$P2 /dev/mapper/_bia_m0 /dev/mapper/_bia_d0
+mount_all
+cp "$SIG" "$T_TMPDIR/m0/sig"
+verify "v4 initial"
+umount_all
+
+echo "== change-quorum-config rejects mixed v4/v6 quorum"
+t_rc scoutfs change-quorum-config --offline -Q 0,127.0.0.1,$P0 -Q 1,::1,$P1 -Q 2,127.0.0.1,$P2 /dev/mapper/_bia_m0
+
+echo "== switch v4 -> v6, signature survives, cross-mount write again"
+t_quiet scoutfs change-quorum-config --offline -Q 0,::1,$P0 -Q 1,::1,$P1 -Q 2,::1,$P2 /dev/mapper/_bia_m0
+mount_all
+verify "after v4->v6"
+cp "$SIG" "$T_TMPDIR/m1/sig-v6"
+cmp -s "$SIG" "$T_TMPDIR/m0/sig-v6" || t_fail "v6 cross-mount write not visible on m0"
+cmp -s "$SIG" "$T_TMPDIR/m2/sig-v6" || t_fail "v6 cross-mount write not visible on m2"
+umount_all
+
+echo "== switch v6 -> v4, signatures survive"
+t_quiet scoutfs change-quorum-config --offline -Q 0,127.0.0.1,$P0 -Q 1,127.0.0.1,$P1 -Q 2,127.0.0.1,$P2 /dev/mapper/_bia_m0
+mount_all
+verify "after v6->v4"
+cmp -s "$SIG" "$T_TMPDIR/m0/sig-v6" || t_fail "after v6->v4 sig-v6 lost"
+umount_all
+
+t_pass
diff --git a/utils/src/quorum.c b/utils/src/quorum.c
index b2b13565..3748b120 100644
--- a/utils/src/quorum.c
+++ b/utils/src/quorum.c
@@ -20,11 +20,20 @@ bool valid_quorum_slots(struct scoutfs_quorum_slot *slots)
 	bool valid = true;
 	char *addr;
 	char ip6addr[INET6_ADDRSTRLEN];
+	__le16 family = cpu_to_le16(SCOUTFS_AF_NONE);
 	int i;
 	int j;
 
 	for (i = 0; i < SCOUTFS_QUORUM_MAX_SLOTS; i++) {
 		if (slots[i].addr.v4.family == cpu_to_le16(SCOUTFS_AF_IPV4)) {
+			if (family == cpu_to_le16(SCOUTFS_AF_NONE)) {
+				family = cpu_to_le16(SCOUTFS_AF_IPV4);
+			} else if (family != cpu_to_le16(SCOUTFS_AF_IPV4)) {
+				fprintf(stderr, "quorum slot nr %u is IPv4 but earlier slots are IPv6; mixed IPv4/IPv6 quorum is not supported\n",
+					i);
+				valid = false;
+			}
+
 			for (j = i + 1; j < SCOUTFS_QUORUM_MAX_SLOTS; j++) {
 				if (slots[i].addr.v4.addr == slots[j].addr.v4.addr &&
 				    slots[i].addr.v4.port == slots[j].addr.v4.port) {
@@ -38,6 +47,14 @@ bool valid_quorum_slots(struct scoutfs_quorum_slot *slots)
 				}
 			}
 		} else if (slots[i].addr.v6.family == cpu_to_le16(SCOUTFS_AF_IPV6)) {
+			if (family == cpu_to_le16(SCOUTFS_AF_NONE)) {
+				family = cpu_to_le16(SCOUTFS_AF_IPV6);
+			} else if (family != cpu_to_le16(SCOUTFS_AF_IPV6)) {
+				fprintf(stderr, "quorum slot nr %u is IPv6 but earlier slots are IPv4; mixed IPv4/IPv6 quorum is not supported\n",
+					i);
+				valid = false;
+			}
+
 			for (j = i + 1; j < SCOUTFS_QUORUM_MAX_SLOTS; j++) {
 				if ((IN6_ARE_ADDR_EQUAL(slots[i].addr.v6.addr, slots[j].addr.v6.addr)) &&
 				    (slots[i].addr.v6.port == slots[j].addr.v6.port)) {