diff --git a/acconfig.h b/acconfig.h
index a62bdc35..e3366488 100644
--- a/acconfig.h
+++ b/acconfig.h
@@ -9,3 +9,6 @@
 
 /* Define this if the C library defines the variable `_sys_siglist'.  */
 #undef HAVE__SYS_SIGLIST
+
+/* Define this if you have the `union wait' type in <sys/wait.h>.  */
+#undef HAVE_UNION_WAIT