diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index b34bf48..1a11a41 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -8416,6 +8416,8 @@
 timers			Compiled with |timer_start()| support.
 title			Compiled with window title support |'title'|.
 toolbar			Compiled with support for |gui-toolbar|.
+ttyin			input is a terminal (tty)
+ttyout			output is a terminal (tty)
 unix			Unix version of Vim.
 user_commands		User-defined commands.
 vertsplit		Compiled with vertically split windows |:vsplit|.