diff --git a/tftpd.h b/tftpd.h
index 945065e..4c2f214 100644
--- a/tftpd.h
+++ b/tftpd.h
@@ -46,7 +46,7 @@ struct thread_data {
      char *mc_addr;             /* multicast address */
      struct sockaddr_storage sa_mcast;
      union ip_mreq_storage mcastaddr;
-     u_char mcast_ttl;
+     unsigned char mcast_ttl;
      
      /*
       * Self can read/write until client_ready is set. Then only allowed to read.
