diff --git a/TimeSeries.pm b/TimeSeries.pm
index fff1ad0..e429a7e 100644
--- a/TimeSeries.pm
+++ b/TimeSeries.pm
@@ -27,7 +27,7 @@ use Data::Dumper;
 use HTTP::Date qw(parse_date);
 use Time::Local qw(timegm_nocheck);
 
-$VERSION = do { my @r=(q$Revision: 1.13 $=~/\d+/g);sprintf "%d."."%02d"x$#r,@r};
+$VERSION = do { my @r=(q$Revision: 1.14 $=~/\d+/g);sprintf "%d."."%02d"x$#r,@r};
 
 =head2 new(%opts)
 
@@ -330,7 +330,7 @@ sub plot {
 	    }
 	} else {
 	    for my $j (@$data) {
-		print $datafh "\t", ($j || 0) + 0;
+		print $datafh "\t", (defined $j ? $j : '?');
 	    }
 	}
 	print $datafh "\n";
@@ -349,6 +349,7 @@ sub plot {
     print $ctlfh "set log x\n" if ($self->{log_x});
     print $ctlfh "set log y\n" if ($self->{log_y});
     print $ctlfh "set key $self->{legend_position}\n" if ($self->{legend_position});
+    print $ctlfh "set datafile missing '?'\n";
 
     # compute ticks
 
@@ -522,7 +523,7 @@ sub plot {
 	} else {
 	    $comma = 1;
 	}
-	print $ctlfh "'$datafn' using 1:", $col++, " title '$i'";
+	print $ctlfh "'$datafn' using 1:(\$", $col++, ") title '$i'";
     }
 
     print $ctlfh "\n";
diff --git a/t/3missing.t b/t/3missing.t
new file mode 100644
index 0000000..aace333
--- /dev/null
+++ b/t/3missing.t
@@ -0,0 +1,41 @@
+#!/usr/bin/perl
+use warnings;
+use strict;
+use Test::More tests => 3;
+
+BEGIN { use_ok( 'TimeSeries' ); }
+
+
+my $ts = TimeSeries->new(output_format => 'ps');
+ok($ts, 			'create timeseries');
+$ts->add(0, 100);
+$ts->add(1000, 200);
+$ts->add(2000, 100);
+$ts->add(3000, undef);
+$ts->add(4000, 100);
+$ts->add(5000, 200);
+$ts->add(6000, 100);
+$ts->legend('missing');
+my $p = $ts->plot();
+my $t = "LT0
+6395 4739 M
+399 0 V
+574 1344 M
+1639 4872 L
+2703 1344 L
+2130 0 R
+5897 4872 L
+6962 1344 L
+1.000 UL
+LTb
+574 1344 M
+6388 0 V
+0 3528 V
+-6388 0 V
+0 -3528 V
+1.000 UP
+stroke";
+ok(index($p, $t) != -1,		'postscript output looks ok');
+
+#vim:tw=0
+