diff --git a/etc/NEWS b/etc/NEWS
index c96e01d26d2..5ed551caeaf 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1218,6 +1218,15 @@ in the presence of files with negative time stamps.
 ** The cars of the elements in `interpreter-mode-alist' are now
 treated as regexps rather than literal strings.
 
+---
+** Overlay priority does not have to be nil or a non-negative integer.
+Overlay priority can be other kinds of Lisp objects.  We didn't yet
+decide whether other types of values are stable enough, and therefore
+don't feel it's right to document them.  For now, don't assume in your
+code that the values of overlay priority can only be either nil or an
+integer, always test them with an appropriate predicate to be one or
+the other.
+
 
 * Lisp Changes in Emacs 24.4