diff --git a/src/s/hpux11.h b/src/s/hpux11.h
index 893e0874eaf..776f8ec2b83 100644
--- a/src/s/hpux11.h
+++ b/src/s/hpux11.h
@@ -9,3 +9,7 @@
 
 /* SA_RESTART resets the timeout of `select', so don't use it.  */
 #define BROKEN_SA_RESTART
+
+/* It does work on HPUX to open the pty's tty in the parent (Emacs),
+   then close and reopen it in the child.  */
+#define USG_SUBTTY_WORKS