diff --git a/gatk.wdl b/gatk.wdl
index 60b81cd8eabac7e2b0b56f8e50c6458f6f6bd5cf..ce8d4c46c8a66f9c3d7ea5d94dc2bbd4246fa38c 100644
--- a/gatk.wdl
+++ b/gatk.wdl
@@ -95,7 +95,7 @@ task CombineGVCFs {
     input {
         Array[File]+ gvcfFiles
         Array[File]+ gvcfFilesIndex
-        Array[File]+ intervals
+        Array[File] intervals = []
         String outputPath
         File referenceFasta
         File referenceFastaDict
@@ -114,7 +114,7 @@ task CombineGVCFs {
         -R ~{referenceFasta} \
         -O ~{outputPath} \
         -V ~{sep=' -V ' gvcfFiles} \
-        -L ~{sep=' -L ' intervals}
+        ~{true='-L' false='' length(intervals) > 0} ~{sep=' -L ' intervals}
     }
 
     output {