diff --git a/driveGnuPlots.pl b/driveGnuPlots.pl
index 109ed77..16d7cba 100755
--- a/driveGnuPlots.pl
+++ b/driveGnuPlots.pl
@@ -34,7 +34,7 @@ GetOptions(\%options,
            "ylabel=s",
            "y2label=s",
            "title=s",
-           "xlen=i",
+           "xlen=f",
            "ymin=f",
            "ymax=f",
            "y2min=f",