diff --git a/slirp/tcp_output.c b/slirp/tcp_output.c
index 779314bf9a..8aa3d90470 100644
--- a/slirp/tcp_output.c
+++ b/slirp/tcp_output.c
@@ -47,6 +47,7 @@ static const u_char  tcp_outflags[TCP_NSTATES] = {
 };
 
 
+#undef MAX_TCPOPTLEN
 #define MAX_TCPOPTLEN	32	/* max # bytes that go in options */
 
 /*