diff --git a/src/schema/vocab.rnc b/src/schema/vocab.rnc
index a696ceb8871f31e39b2abc340baccacc915c3d07..b598401fde0573c1ad5fbc7763a64aca568132c0 100644
--- a/src/schema/vocab.rnc
+++ b/src/schema/vocab.rnc
@@ -31,6 +31,7 @@ skos.Concept =
     & skos.notation?
     & skos.inScheme
     & skos.match
+    & skos.hierarchy
     & empty
    }
 
@@ -57,9 +58,6 @@ skos.match =
    element skos:relatedMatch {
       rdfResource
    }*
- & element skos:broader {
-      rdfResource
-   }*
  & element skos:related {
     rdfResource
  }*
@@ -70,4 +68,8 @@ skos.match =
 skos.altLabel = element skos:altLabel {
    attribute xml:lang { xsd:language }?,
    text
-}
\ No newline at end of file
+}
+
+skos.hierarchy =
+   element skos:broader { rdfResource }
+ & element skos:narrower { rdfResource }