diff --git a/public/biopet-core/src/main/scala/nl/lumc/sasc/biopet/core/Reference.scala b/public/biopet-core/src/main/scala/nl/lumc/sasc/biopet/core/Reference.scala
index 94f511f7a8207c043b5e306149a3abe92e172a07..6a39ca3eb9c68205cf1b5354829b4bb87944bfa9 100644
--- a/public/biopet-core/src/main/scala/nl/lumc/sasc/biopet/core/Reference.scala
+++ b/public/biopet-core/src/main/scala/nl/lumc/sasc/biopet/core/Reference.scala
@@ -83,8 +83,8 @@ trait Reference extends Configurable {
       val defaults = ConfigUtils.mergeMaps(this.defaults, this.internalDefaults)
 
       def getReferences(map: Map[String, Any]): Set[(String, String)] = (for (
-        (species, species_content: Map[String, Any]) <- map.getOrElse("references", Map[String, Any]()).asInstanceOf[Map[String, Any]].toList;
-        (reference_name, _) <- species_content.toList
+        (species, species_content) <- map.getOrElse("references", Map[String, Any]()).asInstanceOf[Map[String, Any]].toList;
+        (reference_name, _) <- species_content.asInstanceOf[Map[String, Any]].toList
       ) yield (species, reference_name)).toSet
 
       val references = getReferences(defaults) ++ getReferences(Config.global.map)