diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index c3e894f..c009494 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -9648,6 +9648,9 @@
 		range overlaps with another.
 		Only characters with value 0x100 and higher can be used.
 
+		If the new value causes 'fillchars' or 'listchars' to become
+		invalid it is rejected and an error is given.
+
 		To clear the overrides pass an empty list: >
 		   setcellwidths([]);
 <		You can use the script $VIMRUNTIME/tools/emoji_list.vim to see