diff --git a/include/haproxy/connection.h b/include/haproxy/connection.h
index 5d9b5ca74..bc26f73b5 100644
--- a/include/haproxy/connection.h
+++ b/include/haproxy/connection.h
@@ -220,6 +220,7 @@ static inline void conn_sock_read0(struct connection *c)
 		/* we don't risk keeping ports unusable if we found the
 		 * zero from the other side.
 		 */
+		BUG_ON(c->flags & CO_FL_FDLESS);
 		HA_ATOMIC_AND(&fdtab[c->handle.fd].state, ~FD_LINGER_RISK);
 	}
 }
@@ -236,6 +237,7 @@ static inline void conn_sock_shutw(struct connection *c, int clean)
 		/* don't perform a clean shutdown if we're going to reset or
 		 * if the shutr was already received.
 		 */
+		BUG_ON(c->flags & CO_FL_FDLESS);
 		if (!(c->flags & CO_FL_SOCK_RD_SH) && clean)
 			shutdown(c->handle.fd, SHUT_WR);
 	}
diff --git a/src/check.c b/src/check.c
index da2deab37..7e6430f05 100644
--- a/src/check.c
+++ b/src/check.c
@@ -744,6 +744,8 @@ static int retrieve_errno_from_socket(struct connection *conn)
 	if (!conn_ctrl_ready(conn))
 		return 0;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (getsockopt(conn->handle.fd, SOL_SOCKET, SO_ERROR, &skerr, &lskerr) == 0)
 		errno = skerr;
 
diff --git a/src/connection.c b/src/connection.c
index af453a6b8..b666d1876 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -809,6 +809,8 @@ int conn_recv_proxy(struct connection *conn, int flag)
 	if (!conn_ctrl_ready(conn))
 		goto fail;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_recv_ready(conn->handle.fd))
 		goto not_ready;
 
@@ -1188,6 +1190,8 @@ int conn_recv_netscaler_cip(struct connection *conn, int flag)
 	if (!conn_ctrl_ready(conn))
 		goto fail;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_recv_ready(conn->handle.fd))
 		goto not_ready;
 
@@ -1454,6 +1458,8 @@ int conn_recv_socks4_proxy_response(struct connection *conn)
 	if (!conn_ctrl_ready(conn))
 		goto fail;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_recv_ready(conn->handle.fd))
 		goto not_ready;
 
diff --git a/src/raw_sock.c b/src/raw_sock.c
index 7ee5f9bc7..553375bb5 100644
--- a/src/raw_sock.c
+++ b/src/raw_sock.c
@@ -59,6 +59,8 @@ int raw_sock_to_pipe(struct connection *conn, void *xprt_ctx, struct pipe *pipe,
 	if (!conn_ctrl_ready(conn))
 		return 0;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_recv_ready(conn->handle.fd))
 		return 0;
 
@@ -172,6 +174,8 @@ int raw_sock_from_pipe(struct connection *conn, void *xprt_ctx, struct pipe *pip
 	if (!conn_ctrl_ready(conn))
 		return 0;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_send_ready(conn->handle.fd))
 		return 0;
 
@@ -231,6 +235,8 @@ static size_t raw_sock_to_buf(struct connection *conn, void *xprt_ctx, struct bu
 	if (!conn_ctrl_ready(conn))
 		return 0;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_recv_ready(conn->handle.fd))
 		return 0;
 
@@ -350,6 +356,8 @@ static size_t raw_sock_from_buf(struct connection *conn, void *xprt_ctx, const s
 	if (!conn_ctrl_ready(conn))
 		return 0;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_send_ready(conn->handle.fd))
 		return 0;
 
diff --git a/src/sock.c b/src/sock.c
index ae825fc02..5afa59f33 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -702,6 +702,7 @@ void sock_accept_iocb(int fd)
  */
 void sock_conn_ctrl_init(struct connection *conn)
 {
+	BUG_ON(conn->flags & CO_FL_FDLESS);
 	fd_insert(conn->handle.fd, conn, sock_conn_iocb, tid_bit);
 }
 
@@ -711,6 +712,7 @@ void sock_conn_ctrl_init(struct connection *conn)
  */
 void sock_conn_ctrl_close(struct connection *conn)
 {
+	BUG_ON(conn->flags & CO_FL_FDLESS);
 	fd_delete(conn->handle.fd);
 	conn->handle.fd = DEAD_FD_MAGIC;
 }
@@ -736,6 +738,8 @@ int sock_conn_check(struct connection *conn)
 	if (!(conn->flags & CO_FL_WAIT_L4_CONN))
 		return 1; /* strange we were called while ready */
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (!fd_send_ready(fd) && !(fdtab[fd].state & (FD_POLL_ERR|FD_POLL_HUP)))
 		return 0;
 
@@ -901,6 +905,8 @@ int sock_drain(struct connection *conn)
 	int fd = conn->handle.fd;
 	int len;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (fdtab[fd].state & (FD_POLL_ERR|FD_POLL_HUP))
 		goto shut;
 
@@ -953,6 +959,8 @@ int sock_check_events(struct connection *conn, int event_type)
 {
 	int ret = 0;
 
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (event_type & SUB_RETRY_RECV) {
 		if (fd_recv_ready(conn->handle.fd))
 			ret |= SUB_RETRY_RECV;
@@ -975,6 +983,8 @@ int sock_check_events(struct connection *conn, int event_type)
  */
 void sock_ignore_events(struct connection *conn, int event_type)
 {
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	if (event_type & SUB_RETRY_RECV)
 		fd_stop_recv(conn->handle.fd);
 
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index 748ab1324..00c35d857 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -5849,6 +5849,8 @@ static int ssl_sock_handshake(struct connection *conn, unsigned int flag)
 	 * the xprt layers should provide some status indicating their knowledge
 	 * of shutdowns or error.
 	 */
+	BUG_ON(conn->flags & CO_FL_FDLESS);
+
 	skerr = 0;
 	lskerr = sizeof(skerr);
 	if ((getsockopt(conn->handle.fd, SOL_SOCKET, SO_ERROR, &skerr, &lskerr) < 0) ||