diff --git a/UPGRADE-6.0.md b/UPGRADE-6.0.md
index b79d74ee2509..c92e3a6312e4 100644
--- a/UPGRADE-6.0.md
+++ b/UPGRADE-6.0.md
@@ -98,3 +98,8 @@ Security
  * Removed `ROLE_PREVIOUS_ADMIN` role in favor of `IS_IMPERSONATOR` attribute
  * Removed `LogoutSuccessHandlerInterface` and `LogoutHandlerInterface`, register a listener on the `LogoutEvent` event instead.
  * Removed `DefaultLogoutSuccessHandler` in favor of `DefaultLogoutListener`.
+
+Yaml
+----
+
+ * Removed support for using the `!php/object` and `!php/const` tags without a value.