diff --git a/src/schema/common.rnc b/src/schema/common.rnc
index 079213b58d900f9fa836e668bccb59bf7b42c30c..d1a7bf51a01bc74a40ada55158ba7b775dc32123 100644
--- a/src/schema/common.rnc
+++ b/src/schema/common.rnc
@@ -35,6 +35,7 @@ optionalMetadata =
  & element dct:description { rdfLiteral }*
  & element dct:title { rdfLiteral }*
  & element dct:relation { rdfResource }*
+ & element dct:source { rdfResource }*
 
 requiredMetadata =
    element dct:publisher { Agent }