diff --git a/workflows/prefactor_calibrator.cwl b/workflows/prefactor_calibrator.cwl
index 96b939cc35d21eb06d0d93c3ca36d1923e43f2f6..cad838d7989c19b9cefba2e859ee8acac6b2e236 100644
--- a/workflows/prefactor_calibrator.cwl
+++ b/workflows/prefactor_calibrator.cwl
@@ -28,6 +28,7 @@ inputs:
     'sbg:y': -411
   - id: baselines_to_flag
     type: 'string[]'
+    default: []
     'sbg:x': -635.8651123046875
     'sbg:y': -148
   - id: uvw