diff --git a/vars/dataset.groovy b/vars/dataset.groovy
index 730b580..965d33b 100644
--- a/vars/dataset.groovy
+++ b/vars/dataset.groovy
@@ -7,7 +7,7 @@
         String credentials = config['credentials']
         String baseURI = config['base_uri']
 
-        def draftset = drafter.findDraftset(PMD, credentials, env.JOB_NAME) // assume it already exists
+        def draftset = drafter.findDraftset(PMD, credentials, env.JOB_NAME as String) // assume it already exists
 
         String datasetPath = util.slugise(datasetLabel)
         String datasetGraph = "${baseURI}/graph/${datasetPath}"