1 files changed, 2 insertions, 1 deletions

diff --git a/src/charset.c b/src/charset.c
index 2ddb1b407dd..ffe0cd9485b 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -1265,7 +1265,8 @@ DEFUN ("string-width", Fstring_width, Sstring_width, 1, 1, 0,
 Width is measured by how many columns it occupies on the screen.\n\
 When calculating width of a multibyte character in STRING,\n\
 only the base leading-code is considered; the validity of\n\
-the following bytes is not checked.")
+the following bytes is not checked.  Tabs in STRING are always\n\
+taken to occupy `tab-width' columns.")
   (str)
      Lisp_Object str;
 {