diff --git a/biopet-extensions/src/main/scala/nl/lumc/sasc/biopet/extensions/Star.scala b/biopet-extensions/src/main/scala/nl/lumc/sasc/biopet/extensions/Star.scala
index 04d2a39b68adc2fc8b70ea1018ee6e168d2eac0c..8cda600b2c578ab430df48548e41fb89a71207ef 100644
--- a/biopet-extensions/src/main/scala/nl/lumc/sasc/biopet/extensions/Star.scala
+++ b/biopet-extensions/src/main/scala/nl/lumc/sasc/biopet/extensions/Star.scala
@@ -75,6 +75,7 @@ class Star(val root: Configurable) extends BiopetCommandLineFunction with Refere
   var genomeSAindexNbases: Option[Int] = config("genomesaindexnbases")
   var genomeSAsparseD: Option[Int] = config("genomesasparsed")
 
+  @Input(required = false)
   var sjdbGTFfile: Option[File] = config("sjdbgtfile")
   var sjdbGTFchrPrefix: Option[String] = config("sjdbgtfchrprefix")
   var sjdbGTFfeatureExon: Option[String] = config("sjdbgtffeatureexon")