Index: uspace/srv/net/tcp/sock.c
===================================================================
--- uspace/srv/net/tcp/sock.c	(revision e1c0260111c18cf291351f04dd1cc7118051fbdc)
+++ uspace/srv/net/tcp/sock.c	(revision c92e30fd4c782868f0f4d1b8087da611f1efa90a)
@@ -779,4 +779,9 @@
 	}
 
+	/* Grab recv_buffer_lock because of CV wait in tcp_sock_recv_fibril() */
+	fibril_mutex_lock(&socket->recv_buffer_lock);
+	socket->sock_core = NULL;
+	fibril_mutex_unlock(&socket->recv_buffer_lock);
+
 	rc = socket_destroy(NULL, socket_id, &client->sockets, &gsock,
 	    tcp_free_sock_data);
@@ -839,8 +844,9 @@
 	log_msg(LVL_DEBUG, "tcp_sock_recv_fibril()");
 
+	fibril_mutex_lock(&sock->recv_buffer_lock);
+
 	while (true) {
 		log_msg(LVL_DEBUG, "call tcp_uc_receive()");
-		fibril_mutex_lock(&sock->recv_buffer_lock);
-		while (sock->recv_buffer_used != 0)
+		while (sock->recv_buffer_used != 0 && sock->sock_core != NULL)
 			fibril_condvar_wait(&sock->recv_buffer_cv,
 			    &sock->recv_buffer_lock);
@@ -852,6 +858,6 @@
 			sock->recv_error = trc;
 			fibril_condvar_broadcast(&sock->recv_buffer_cv);
-			fibril_mutex_unlock(&sock->recv_buffer_lock);
-			tcp_sock_notify_data(sock->sock_core);
+			if (sock->sock_core != NULL)
+				tcp_sock_notify_data(sock->sock_core);
 			break;
 		}
@@ -861,7 +867,9 @@
 		sock->recv_buffer_used = data_len;
 		fibril_condvar_broadcast(&sock->recv_buffer_cv);
-		fibril_mutex_unlock(&sock->recv_buffer_lock);
-		tcp_sock_notify_data(sock->sock_core);
-	}
+		if (sock->sock_core != NULL)
+			tcp_sock_notify_data(sock->sock_core);
+	}
+
+	fibril_mutex_unlock(&sock->recv_buffer_lock);
 
 	tcp_uc_delete(sock->conn);