diff --git a/include/haproxy/protocol-t.h b/include/haproxy/protocol-t.h
index fde7590a48..838c7c31c1 100644
--- a/include/haproxy/protocol-t.h
+++ b/include/haproxy/protocol-t.h
@@ -70,7 +70,17 @@ enum proto_type {
 #define PROTO_F_REUSEPORT_TESTED                0x00000002 /* SO_REUSEPORT support was tested */
 
 /* protocol families define standard functions acting on a given address family
- * for a socket implementation, such as AF_INET/PF_INET for example.
+ * for a socket implementation, such as AF_INET/PF_INET for example. There is
+ * permanent confusion between domain and family. Here's how it works:
+ *   - the domain defines the format of addresses (e.g. sockaddr_in etc),
+ *     it is passed as the first argument to socket()
+ *   - the family is part of the address and is stored in receivers, servers
+ *     and everywhere there is an address. It's also a proto_fam selector.
+ * Domains are often PF_xxx though man 2 socket on Linux quotes 4.x BSD's man
+ * that says AF_* can be used everywhere. At least it tends to keep the code
+ * clearer about the intent. In HAProxy we're defining new address families
+ * with AF_CUST_* which appear in addresses, and they cannot be used for the
+ * domain, the socket() call must use sock_domain instead.
  */
 struct proto_fam {
 	char name[PROTO_NAME_LEN];                      /* family name, zero-terminated */
diff --git a/src/proto_rhttp.c b/src/proto_rhttp.c
index 0bf5bdc511..e831a59365 100644
--- a/src/proto_rhttp.c
+++ b/src/proto_rhttp.c
@@ -22,8 +22,8 @@
 
 struct proto_fam proto_fam_rhttp = {
 	.name = "rhttp",
-	.sock_domain = AF_CUST_RHTTP_SRV,
-	.sock_family = AF_INET,
+	.sock_domain = AF_INET,
+	.sock_family = AF_CUST_RHTTP_SRV,
 	.bind = rhttp_bind_receiver,
 };
 
diff --git a/src/proto_sockpair.c b/src/proto_sockpair.c
index a719063a81..69ab45cfcb 100644
--- a/src/proto_sockpair.c
+++ b/src/proto_sockpair.c
@@ -50,8 +50,8 @@ struct connection *sockpair_accept_conn(struct listener *l, int *status);
 
 struct proto_fam proto_fam_sockpair = {
 	.name = "sockpair",
-	.sock_domain = AF_CUST_SOCKPAIR,
-	.sock_family = AF_UNIX,
+	.sock_domain = AF_UNIX,
+	.sock_family = AF_CUST_SOCKPAIR,
 	.sock_addrlen = sizeof(struct sockaddr_un),
 	.l3_addrlen = sizeof(((struct sockaddr_un*)0)->sun_path),
 	.addrcmp = NULL,
diff --git a/src/protocol.c b/src/protocol.c
index 399835a887..69f4595bb2 100644
--- a/src/protocol.c
+++ b/src/protocol.c
@@ -38,14 +38,14 @@ __decl_spinlock(proto_lock);
 /* Registers the protocol <proto> */
 void protocol_register(struct protocol *proto)
 {
-	int sock_domain = proto->fam->sock_domain;
+	int sock_family = proto->fam->sock_family;
 
-	BUG_ON(sock_domain < 0 || sock_domain >= AF_CUST_MAX);
+	BUG_ON(sock_family < 0 || sock_family >= AF_CUST_MAX);
 	BUG_ON(proto->proto_type >= PROTO_NUM_TYPES);
 
 	HA_SPIN_LOCK(PROTO_LOCK, &proto_lock);
 	LIST_APPEND(&protocols, &proto->list);
-	__protocol_by_family[sock_domain]
+	__protocol_by_family[sock_family]
 	                    [proto->proto_type]
 	                    [proto->xprt_type == PROTO_TYPE_DGRAM] = proto;
 	HA_SPIN_UNLOCK(PROTO_LOCK, &proto_lock);
diff --git a/src/sock.c b/src/sock.c
index df82c6ea7b..61ebf4a929 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -1147,7 +1147,7 @@ int _sock_supports_reuseport(const struct proto_fam *fam, int type, int protocol
 	fd1 = fd2 = -1;
 
 	/* ignore custom sockets */
-	if (!fam || fam->sock_domain >= AF_MAX)
+	if (!fam || fam->sock_family >= AF_MAX)
 		goto leave;
 
 	fd1 = socket(fam->sock_domain, type, protocol);