diff --git a/src/microhttpd/daemon.c b/src/microhttpd/daemon.c
index a5d2d296..4999da50 100644
--- a/src/microhttpd/daemon.c
+++ b/src/microhttpd/daemon.c
@@ -5844,7 +5844,7 @@ MHD_start_daemon_va (unsigned int flags,
         if (0 != setsockopt (listen_fd,
                              IPPROTO_TCP,
                              TCP_FASTOPEN,
-                             &daemon->fastopen_queue_size,
+                             (const void*)&daemon->fastopen_queue_size,
                              sizeof (daemon->fastopen_queue_size)))
         {
 #ifdef HAVE_MESSAGES