diff --git a/src/s/usg5-4.h b/src/s/usg5-4.h
index ebb848199eb..8681cee6acc 100644
--- a/src/s/usg5-4.h
+++ b/src/s/usg5-4.h
@@ -137,7 +137,9 @@ Boston, MA 02111-1307, USA.  */
    subprocesses the usual way.  But TIOCSIGNAL does work for PTYs, and
    this is all we need.  */
 
+#ifndef IRIX6
 #define TIOCSIGSEND TIOCSIGNAL
+#endif
 
 /* This change means that we don't loop through allocate_pty too many
    times in the (rare) event of a failure. */
@@ -198,6 +200,8 @@ Boston, MA 02111-1307, USA.  */
    So give it a try.  */
 #define HAVE_SOCKETS
 
+#ifndef IRIX6
 #define bcopy(src,dst,n)	memmove (dst,src,n)
 #define bcmp(src,dst,n)		memcmp (src,dst,n)
 #define bzero(s,n)		memset (s,0,n)
+#endif