diff --git a/acconfig.h b/acconfig.h
index 40f3a53d0..d12ee8e72 100644
--- a/acconfig.h
+++ b/acconfig.h
@@ -13,9 +13,15 @@
 #undef HAVE_U_INT32_T
 #undef HAVE_U_INT64_T
 
+/* Define this to the type ssize_t should be */
 #undef ssize_t
+
+/* Define this to the type sig_atomic_t should be */
 #undef sig_atomic_t
 
+/* Define this to the type mode_t should be */
+#undef mode_t
+
 /*  Define this if struct utmp have ut_user  */
 #undef HAVE_UT_USER