diff --git a/library/Icinga/Less/Visitor.php b/library/Icinga/Less/Visitor.php
index a28379692..347d1bbbc 100644
--- a/library/Icinga/Less/Visitor.php
+++ b/library/Icinga/Less/Visitor.php
@@ -92,6 +92,8 @@ class Visitor extends Less_VisitorReplacing
             $p['value'] = $this->visitObj($p['value']);
         }
 
+        $m->rules = $this->visitArray($m->rules);
+
         $this->definingMixin = spl_object_hash($m);
 
         return $m;