diff --git a/kmod/src/format.h b/kmod/src/format.h
index 28a15175..70ea4ded 100644
--- a/kmod/src/format.h
+++ b/kmod/src/format.h
@@ -86,11 +86,33 @@ struct scoutfs_timespec {
 	__u8 __pad[4];
 };
 
-/* XXX ipv6 */
-struct scoutfs_inet_addr {
-	__le32 addr;
+enum scoutfs_inet_family {
+	SCOUTFS_AF_NONE = 0,
+	SCOUTFS_AF_IPV4 = 1,
+	SCOUTFS_AF_IPV6 = 2,
+};
+
+struct scoutfs_inet_addr4 {
+	__le16 family;
 	__le16 port;
-	__u8 __pad[2];
+	__le32 addr;
+};
+
+/*
+ * Not yet supported by code.
+ */
+struct scoutfs_inet_addr6 {
+	__le16 family;
+	__le16 port;
+	__u8 addr[16];
+	__le32 flow_info;
+	__le32 scope_id;
+	__u8 __pad[4];
+};
+
+union scoutfs_inet_addr {
+	struct scoutfs_inet_addr4 v4;
+	struct scoutfs_inet_addr6 v6;
 };
 
 /*
@@ -591,7 +613,7 @@ struct scoutfs_quorum_message {
 struct scoutfs_quorum_config {
 	__le64 version;
 	struct scoutfs_quorum_slot {
-		struct scoutfs_inet_addr addr;
+		union scoutfs_inet_addr addr;
 	} slots[SCOUTFS_QUORUM_MAX_SLOTS];
 };
 
diff --git a/kmod/src/net.h b/kmod/src/net.h
index 05e9c3be..0b18b6ff 100644
--- a/kmod/src/net.h
+++ b/kmod/src/net.h
@@ -90,19 +90,13 @@ enum conn_flags {
 #define SIN_ARG(sin)	sin, be16_to_cpu((sin)->sin_port)
 
 static inline void scoutfs_addr_to_sin(struct sockaddr_in *sin,
-				       struct scoutfs_inet_addr *addr)
+				       union scoutfs_inet_addr *addr)
 {
-	sin->sin_family = AF_INET;
-	sin->sin_addr.s_addr = cpu_to_be32(le32_to_cpu(addr->addr));
-	sin->sin_port = cpu_to_be16(le16_to_cpu(addr->port));
-}
+	BUG_ON(addr->v4.family != cpu_to_le16(SCOUTFS_AF_IPV4));
 
-static inline void scoutfs_addr_from_sin(struct scoutfs_inet_addr *addr,
-					 struct sockaddr_in *sin)
-{
-	addr->addr = be32_to_le32(sin->sin_addr.s_addr);
-	addr->port = be16_to_le16(sin->sin_port);
-	memset(addr->__pad, 0, sizeof(addr->__pad));
+	sin->sin_family = AF_INET;
+	sin->sin_addr.s_addr = cpu_to_be32(le32_to_cpu(addr->v4.addr));
+	sin->sin_port = cpu_to_be16(le16_to_cpu(addr->v4.port));
 }
 
 struct scoutfs_net_connection *
diff --git a/kmod/src/quorum.c b/kmod/src/quorum.c
index caff0c2b..c7d50cab 100644
--- a/kmod/src/quorum.c
+++ b/kmod/src/quorum.c
@@ -138,7 +138,7 @@ static bool quorum_slot_present(struct scoutfs_super_block *super, int i)
 {
 	BUG_ON(i < 0 || i > SCOUTFS_QUORUM_MAX_SLOTS);
 
-	return super->qconf.slots[i].addr.addr != 0;
+	return super->qconf.slots[i].addr.v4.family == cpu_to_le16(SCOUTFS_AF_IPV4);
 }
 
 static ktime_t election_timeout(void)
@@ -976,6 +976,9 @@ static int verify_quorum_slots(struct super_block *sb)
 		}
 
 		for (j = i + 1; j < SCOUTFS_QUORUM_MAX_SLOTS; j++) {
+			if (!quorum_slot_present(super, j))
+				continue;
+
 			scoutfs_quorum_slot_sin(super, j, &other);
 
 			if (sin.sin_addr.s_addr == other.sin_addr.s_addr &&
diff --git a/utils/src/mkfs.c b/utils/src/mkfs.c
index eddb3072..c646c8ae 100644
--- a/utils/src/mkfs.c
+++ b/utils/src/mkfs.c
@@ -361,12 +361,12 @@ static int do_mkfs(struct mkfs_args *args)
 		struct scoutfs_quorum_slot *sl = &super->qconf.slots[i];
 		struct in_addr in;
 
-		if (sl->addr.addr == 0)
+		if (sl->addr.v4.family != cpu_to_le16(SCOUTFS_AF_IPV4))
 			continue;
 
-		in.s_addr = htonl(le32_to_cpu(sl->addr.addr));
+		in.s_addr = htonl(le32_to_cpu(sl->addr.v4.addr));
 		printf("%s%u: %s:%u", indent,
-		       i, inet_ntoa(in), le16_to_cpu(sl->addr.port));
+		       i, inet_ntoa(in), le16_to_cpu(sl->addr.v4.port));
 		indent = "\n                        ";
 	}
 	printf("\n");
@@ -395,22 +395,28 @@ static bool valid_quorum_slots(struct scoutfs_quorum_slot *slots)
 	int j;
 
 	for (i = 0; i < SCOUTFS_QUORUM_MAX_SLOTS; i++) {
-		if (slots[i].addr.addr == 0)
+		if (slots[i].addr.v4.family == cpu_to_le16(SCOUTFS_AF_NONE))
 			continue;
 
+		if (slots[i].addr.v4.family != cpu_to_le16(SCOUTFS_AF_IPV4)) {
+			fprintf(stderr, "quorum slot nr %u has invalid family %u\n",
+				i, le16_to_cpu(slots[i].addr.v4.family));
+			valid = false;
+		}
+
 		for (j = i + 1; j < SCOUTFS_QUORUM_MAX_SLOTS; j++) {
-			if (slots[j].addr.addr == 0)
+			if (slots[i].addr.v4.family != cpu_to_le16(SCOUTFS_AF_IPV4))
 				continue;
 
-			if (slots[i].addr.addr == slots[j].addr.addr &&
-			    slots[i].addr.port == slots[j].addr.port) {
+			if (slots[i].addr.v4.addr == slots[j].addr.v4.addr &&
+			    slots[i].addr.v4.port == slots[j].addr.v4.port) {
 
 				in.s_addr =
-					htonl(le32_to_cpu(slots[i].addr.addr));
+					htonl(le32_to_cpu(slots[i].addr.v4.addr));
 				addr = inet_ntoa(in);
 				fprintf(stderr, "quorum slot nr %u and %u have the same address %s:%u\n",
 					i, j, addr,
-					le16_to_cpu(slots[i].addr.port));
+					le16_to_cpu(slots[i].addr.v4.port));
 				valid = false;
 			}
 		}
@@ -430,7 +436,7 @@ static int parse_opt(int key, char *arg, struct argp_state *state)
 		ret = parse_quorum_slot(&slot, arg);
 		if (ret < 0)
 			return ret;
-		if (args->slots[ret].addr.addr != 0)
+		if (args->slots[ret].addr.v4.family != cpu_to_le16(SCOUTFS_AF_NONE))
 			argp_error(state, "Quorum slot %u already specified before slot '%s'\n",
 				   ret, arg);
 		args->slots[ret] = slot;
diff --git a/utils/src/parse.c b/utils/src/parse.c
index 49d566b8..3167a2ff 100644
--- a/utils/src/parse.c
+++ b/utils/src/parse.c
@@ -213,7 +213,8 @@ int parse_quorum_slot(struct scoutfs_quorum_slot *slot, char *arg)
 		return -EINVAL;
 	}
 
-	slot->addr.addr = cpu_to_le32(htonl(in.s_addr));
-	slot->addr.port = cpu_to_le16(port);
+	slot->addr.v4.family = cpu_to_le16(SCOUTFS_AF_IPV4);
+	slot->addr.v4.addr = cpu_to_le32(htonl(in.s_addr));
+	slot->addr.v4.port = cpu_to_le16(port);
 	return nr;
 }
diff --git a/utils/src/print.c b/utils/src/print.c
index 084626f2..10140be6 100644
--- a/utils/src/print.c
+++ b/utils/src/print.c
@@ -769,7 +769,7 @@ static int print_btree_leaf_items(int fd, struct scoutfs_super_block *super,
 	return 0;
 }
 
-static char *alloc_addr_str(struct scoutfs_inet_addr *ia)
+static char *alloc_addr_str(union scoutfs_inet_addr *ia)
 {
 	struct in_addr addr;
 	char *quad;
@@ -777,12 +777,12 @@ static char *alloc_addr_str(struct scoutfs_inet_addr *ia)
 	int len;
 
 	memset(&addr, 0, sizeof(addr));
-	addr.s_addr = htonl(le32_to_cpu(ia->addr));
+	addr.s_addr = htonl(le32_to_cpu(ia->v4.addr));
 	quad = inet_ntoa(addr);
 	if (quad == NULL)
 		return NULL;
 
-	len = snprintf(NULL, 0, "%s:%u", quad, le16_to_cpu(ia->port));
+	len = snprintf(NULL, 0, "%s:%u", quad, le16_to_cpu(ia->v4.port));
 	if (len < 1 || len > 22)
 		return NULL;
 
@@ -791,7 +791,7 @@ static char *alloc_addr_str(struct scoutfs_inet_addr *ia)
 	if (!str)
 		return NULL;
 
-	snprintf(str, len, "%s:%u", quad, le16_to_cpu(ia->port));
+	snprintf(str, len, "%s:%u", quad, le16_to_cpu(ia->v4.port));
 	return str;
 }
 
@@ -915,8 +915,7 @@ static void print_super_block(struct scoutfs_super_block *super, u64 blkno)
 	printf("  quorum config version %llu\n",
 		le64_to_cpu(super->qconf.version));
 	for (i = 0; i < array_size(super->qconf.slots); i++) {
-		if (!super->qconf.slots[i].addr.addr &&
-		    !super->qconf.slots[i].addr.port)
+		if (super->qconf.slots[i].addr.v4.family != cpu_to_le16(SCOUTFS_AF_IPV4))
 			continue;
 
 		addr = alloc_addr_str(&super->qconf.slots[i].addr);