diff --git a/gtk/theme/Adwaita/README b/gtk/theme/Adwaita/README
index a2e97d13d5..e2734ba30d 100644
--- a/gtk/theme/Adwaita/README
+++ b/gtk/theme/Adwaita/README
@@ -5,6 +5,9 @@ Summary
 * To be able to use the latest/adequate version of sass, install sassc
 * The configure script will detect whether or not you have sassc installed;
   if you do, it will regenerate the CSS every time you modify the SCSS files.
+* Note that meson always builds out-of-tree, so the modified css files will
+  appear in your builddir, and you need to copy them back to the srcdir
+  to commit them.
 
 How to tweak the theme
 ----------------------