diff --git a/src/ruleset.rnc b/src/ruleset.rnc
index 98edcbc6d8305845c3ec3be65a4813466e9a76eb..0bb2e0e4f57fa44640851865bca9ee4884ef3557 100644
--- a/src/ruleset.rnc
+++ b/src/ruleset.rnc
@@ -13,6 +13,7 @@ Preferences =
    element Preferences {
       element debug { "0" | "1" }?,
       MetadataTypeDef*,
+      StructTypeDef*,
       ImportExportDef
    }