diff --git a/macs2.wdl b/macs2.wdl
index 4c0125ef8eadb93883f7a589e3e726e71db8e78b..81afcd1b6333ea4d22a94fa7fd038af1cbbc0580 100644
--- a/macs2.wdl
+++ b/macs2.wdl
@@ -14,7 +14,7 @@ task PeakCalling {
         --treatment ${sep = ' ' bamFiles} \
         --outdir ${outDir} \
         --name ${sampleName} \
-        ${default=false true='--nomodel' nomodel}
+        ${default=false true='--nomodel', false='' nomodel}
     }
 
     output {