diff --git a/allanplot.py b/allanplot.py
index 33bfc15..4ba3a95 100644
--- a/allanplot.py
+++ b/allanplot.py
@@ -52,7 +52,7 @@ def main():
     # filename
     filename = args.filename
     # columns
-    columns = args.columns
+    columns = map(int, args.columns)
     # rate
     rate = int(args.rate)