diff --git a/best-practices/README.md b/best-practices/README.md
index 9429de34..c8c6a0a7 100644
--- a/best-practices/README.md
+++ b/best-practices/README.md
@@ -69,6 +69,8 @@ Rails
 * Don't change a migration after it has been merged into master if the desired
   change can be solved with another migration.
 * Don't reference a model class directly from a view.
+* Don't return false from `ActiveModel` callbacks, but instead raise an
+  exception.
 * Don't use instance variables in partials. Pass local variables to partials
   from view templates.
 * Don't use SQL or SQL fragments (`where('inviter_id IS NOT NULL')`) outside of