diff --git a/sphinx/texinputs/LatinRules.xdy b/sphinx/texinputs/LatinRules.xdy
index 99f14a2ee85..f0db7abfe3f 100644
--- a/sphinx/texinputs/LatinRules.xdy
+++ b/sphinx/texinputs/LatinRules.xdy
@@ -1,6 +1,10 @@
-;; style file for xindy
+;; Common Lisp style file for xindy
 ;; filename: LatinRules.xdy
 ;;
+;; Please note that this data file deliberately uses strings
+;; with single non-ascii bytes. This is intentional and
+;; follows the usage observed in similar xindy support files.
+;;
 ;; It is based upon xindy's files lang/general/utf8.xdy and
 ;; lang/general/utf8-lang.xdy which implement
 ;; "a general sorting order for Western European languages"