diff --git a/misc/schema/xrc_schema.rnc b/misc/schema/xrc_schema.rnc
index cab7948175..e48d707586 100644
--- a/misc/schema/xrc_schema.rnc
+++ b/misc/schema/xrc_schema.rnc
@@ -430,7 +430,9 @@ stdWindowProperties =
         [xrc:p="o"] element ownfont {_, t_font }* &
         [xrc:p="o"] element help    {_, t_text }*
 
+# hack: add "feature" to "platform" because it also can be used on any element
 platform =
+        attribute feature  { t_string }? &
         attribute platform {
             xsd:string { pattern = "(win|mac|msw|unix)( *\| *(win|mac|msw|unix))*" }
         }?