diff --git a/README.in b/README.in
index a7863bd06f..e15a52ba1d 100644
--- a/README.in
+++ b/README.in
@@ -90,6 +90,11 @@ Release notes for 3.20
   and gtk_window_set_default_size() to restore the window size. See
   https://wiki.gnome.org/HowDoI/SaveWindowState for a detailed example.
 
+* GtkDrawingArea used to implicitly render the theme background before
+  calling the ::draw handler. This is no longer the case. If you rely
+  on having a theme-provided background, call gtk_render_background()
+  from your ::draw handler.
+
 Release notes for 3.18
 ======================