diff --git a/bedtools.wdl b/bedtools.wdl
index 74b51c006c0cab981fc9dde08da8cebabd0f6c01..3e847d2d8d91f24a84f0e3f65ee50f4cd2955e95 100644
--- a/bedtools.wdl
+++ b/bedtools.wdl
@@ -131,6 +131,8 @@ task MergeBedFiles {
         String outputBed = "merged.bed"
         String dockerImage = "quay.io/biocontainers/bedtools:2.23.0--hdbcaa40_3"
     }
+
+    # A sorted bed is needed for bedtools merge
     command {
         cat ~{sep=" " bedFiles} | bedtools sort | bedtools merge > ~{outputBed}
     }