diff --git a/doc/80-Upgrading.md b/doc/80-Upgrading.md
index 85e89f121..842c281a9 100644
--- a/doc/80-Upgrading.md
+++ b/doc/80-Upgrading.md
@@ -10,6 +10,7 @@ v2.6 to v2.8 requires to follow the instructions for v2.7 too.
 * Asset support for modules (#3961) introduced with v2.8 has now been removed.
 * `expandable-toggle`-support has been removed. Use `class="collapsible" data-visible-height=0`
   to achieve the same effect. (Available since v2.7.0)
+* The `.var()` LESS mixin and the LESS function `extract-variable-default` have been removed (introduced with v2.9)
 
 ## Upgrading to Icinga Web 2 2.9.1