diff --git a/script/pollution.py b/script/pollution.py
index ef8776f..ad99fde 100755
--- a/script/pollution.py
+++ b/script/pollution.py
@@ -261,7 +261,7 @@ if __name__ == '__main__':
     parser.add_argument('-b', '--ref_bed', help="ref_bed", required=True)
     parser.add_argument('-v', '--vcf', help="raw vcf for prbe 160 or 17 ; somatic vcf for prbe 682 or 624",
                         required=True)
-    parser.add_argument('-v2', '--vcf2', help="germline vcf; required when prbe 682 or 624")
+    parser.add_argument('-v2', '--vcf2', help="germline vcf; required when prbe 682 or 624", default='', required=False, nargs='?')
     parser.add_argument('-c', '--cnvkit_bed', help="cnvkit_bed; required when prbe 682 or 624")
     parser.add_argument('-p', '--probe', help="probe, 682, 624, 160, 17 for now ", required=True)
     parser.add_argument('-o', '--output_dir', help="Output directory, default ./", default='')