diff --git a/runtime/doc/vim9.txt b/runtime/doc/vim9.txt
index 576456a..1782f17 100644
--- a/runtime/doc/vim9.txt
+++ b/runtime/doc/vim9.txt
@@ -1,4 +1,4 @@
-*vim9.txt*	For Vim version 8.2.  Last change: 2021 Sep 13
+*vim9.txt*	For Vim version 8.2.  Last change: 2021 Nov 22
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -821,6 +821,10 @@
 
 For loop ~
 
+The loop variable must not exist yet: >
+	var i = 1
+	for i in [1, 2, 3]   # Error!
+
 Legacy Vim script has some tricks to make a for loop over a list handle
 deleting items at the current or previous item.  In Vim9 script it just uses
 the index, if items are deleted then items in the list will be skipped.