diff --git a/macs2.wdl b/macs2.wdl
index 57f75f10a3a14ac406eaaf171430d9158b1dd035..e89a1b7c6f1087937d3d335dd88c528ac7c145ac 100644
--- a/macs2.wdl
+++ b/macs2.wdl
@@ -5,10 +5,10 @@ import "common.wdl"
 task PeakCalling {
     input {
         String? preCommand
-        File inputBams
-        File inputBamsIndex
-        File? controlBams
-        File? controlBamsIndex
+        Array[File]+ inputBams
+        Array[File]+ inputBamsIndex
+        Array[File]+? controlBams
+        Array[File]+? controlBamsIndex
         String outDir
         String sampleName
         Int threads = 1