diff --git a/src/schema/vocab.rnc b/src/schema/vocab.rnc
index aa6e57556b68de9d4aa78b014b68373c1a88dee7..e16c6b40a997ceb7d24bd7cfba8faf01c6f70872 100644
--- a/src/schema/vocab.rnc
+++ b/src/schema/vocab.rnc
@@ -41,7 +41,8 @@ skos.inScheme =
       s:pattern [
          s:rule [
             context = "/rdf:RDF/skos:Concept/skos:inScheme" s:assert [
-               test = "not(empty(/rdf:RDF/skos:ConceptScheme/@rdf:about = current()/@rdf:resource))"
+               test = "/rdf:RDF/skos:ConceptScheme/@rdf:about = current()/@rdf:resource"
+               id = "skos.inScheme_001"
                "Das Konzept muss zu einem Ordnungssystem gehören, dass in dieser Datei definiert ist."
             ]
          ]