diff --git a/Sex.DetERRmine.py b/Sex.DetERRmine.py
index 101708c..28b4348 100755
--- a/Sex.DetERRmine.py
+++ b/Sex.DetERRmine.py
@@ -33,7 +33,7 @@ def CalcErrors(AutSnps, XSnps, YSnps, NrAut, NrX, NrY):
 parser = argparse.ArgumentParser(description="Calculate the relative X- and Y-chromosome coverage of data, as well as the associated error bars for each.")
 parser.add_argument("-I", "--Input", metavar="<INPUT FILE>", type=argparse.FileType('r'), help="The input samtools depth file. Omit to read from stdin.", required=False)
 parser.add_argument("-f", "--SampleList", type=argparse.FileType('r'), help="A list of samples/bams that were in the depth file. One per line. Should be in the order of the samtools depth output.")
-parser.add_argument("-v", "--version", type="store_true", help="Print the version of the script and exit.")
+parser.add_argument("-v", "--version", action="store_true", help="Print the version of the script and exit.")
 args = parser.parse_args()
 
 if args.version: