diff --git a/star.wdl b/star.wdl
index 46d401c178ccfcfc8c6bec5ff574b0d88ec3e96c..ddbf5d58b681aeb3e2935196f78a0870967803ad 100644
--- a/star.wdl
+++ b/star.wdl
@@ -2,7 +2,7 @@ task Star {
     String? preCommand
 
     Array[File] inputR1
-    Array[File]? inputR2
+    Array[File?] inputR2
     String genomeDir
     String outFileNamePrefix