--- t/plplot.t_orig	2011-12-22 12:48:39 +1100
+++ t/plplot.t_new	2011-12-24 12:09:24 +1100
@@ -497,6 +497,18 @@
 SKIP: {
   skip 'Not compiled with POSIX threads', 1 unless ($PDL::Config{WITH_POSIX_THREADS} == 1);
 
+  my $reffile = "test29.$dev";
+  my $pl = PDL::Graphics::PLplot->new(DEV => $dev, FILE => $reffile);
+
+  # Some simple sequential data
+  my $grid_size = 34;
+  my $xs = sequence($grid_size);
+  my $ys = sequence($grid_size)->transpose;
+
+  # Plot data so that increasing y-values have different colors:
+  $pl->xyplot($xs, $ys, PLOTTYPE => 'POINTS', COLORMAP => $ys);
+  $pl->close;
+
   my $pltfile = "test28.$dev";
   if($pid = fork()) {
     $a = waitpid($pid,0);
@@ -526,7 +538,7 @@
   }
 
   # If pthreads are working wrongly, the .svg file is messed up and much larger than usual
-  ok( (-s $pltfile <= 600_000) && (($? & 0xff ) == 0), "Fails to crash with POSIX threads");
+  ok( ((-s $pltfile) == (-s $reffile)) && (($? & 0xff ) == 0), "Fails to crash with POSIX threads");
 
 };