diff --git a/src/s/irix3-3.h b/src/s/irix3-3.h
index 42d6d9d8f62..86a555e9e8c 100644
--- a/src/s/irix3-3.h
+++ b/src/s/irix3-3.h
@@ -179,3 +179,7 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
 
 /* Use setsid to handle terminals for subprocesses.  */
 #define HAVE_SETSID
+
+/* sioctl.h should be included where appropriate.  */
+
+#define NEED_SIOCTL