diff --git a/macs2.wdl b/macs2.wdl
index 2f8d97e9a07eedaa9c795cc39007a3533d9b2439..829741d13bc38cf0f6f919ac76e70aef28e521c5 100644
--- a/macs2.wdl
+++ b/macs2.wdl
@@ -14,7 +14,7 @@ task PeakCalling {
         --treatment ${sep = ' ' bamFiles} \
         --outdir ${outDir} \
         --name ${sampleName} \
-        ${true='--nomodel' false='' default=false nomodel}
+        ${true='--nomodel' false='' default='false' nomodel}
     }
 
     output {