diff --git a/Graph/axestype.pm b/Graph/axestype.pm
index 43ef704..d4e4da7 100644
--- a/Graph/axestype.pm
+++ b/Graph/axestype.pm
@@ -619,7 +619,7 @@ sub setup_x_step_size_v
                 ($s->{true_x_min} - $s->{x_min}) * $delta + $s->{left};
             $s->{x_step} = 
                 ($s->{true_x_max} - $s->{true_x_min}) * 
-                $delta/($s->{_data}->num_points - 1);
+                $delta/($s->{_data}->num_points + 1);
         }
     }
     else
@@ -650,7 +650,7 @@ sub setup_x_step_size_h
                 ($s->{true_x_min} - $s->{x_min}) * $delta + $s->{top};
             $s->{x_step} = 
                 ($s->{true_x_max} - $s->{true_x_min}) * 
-                $delta/($s->{_data}->num_points - 1);
+                $delta/($s->{_data}->num_points + 1);
         }
     }
     else
diff --git a/samples/sample56c.pl b/samples/sample56c.pl
new file mode 100644
index 0000000..525868f
--- /dev/null
+++ b/samples/sample56c.pl
@@ -0,0 +1,49 @@
+use GD::Graph::lines;
+require 'save.pl';
+
+# Test "x_tick_number => 'auto'" without a numeric range.  This particular case
+# used to draw off the right edge of the data area.  -- rgr, 18-May-16.
+
+print STDERR "Processing sample56c (experimental)\n";
+
+my $path = $ENV{GDGRAPH_SAMPLES_PATH} ? $ENV{GDGRAPH_SAMPLES_PATH} : '';
+my $data = [ ['0', '2', '4', '6.25', '8', '10', '12', '14'],
+	     ['432.318842651988', '446.217819254983', '723.746891012408',
+	      '598.379509269257', undef, '265.615817796314',
+	      '471.286904550713', '492.229626240883'],
+	     ['13485.2274536207', '10957.7888732859', '11508.8740865655',
+	      '10904.206172456', undef, '12383.6613029203',
+	      '11969.5663825213', '10364.6735122806'],
+	     ['96570.0967171216', '87353.7950170576', '96274.433424145',
+	      '97911.3638330277', undef, '95467.382370267',
+	      '98499.4608101706', '82889.9385557332'],
+	     ['110487.643013394', '98757.8017095985', '108507.054401723',
+	      '109413.949514753', undef, '108116.659490984',
+	      '110940.314097243', '93746.8416942547']
+    ];
+
+$my_graph = new GD::Graph::lines();
+
+$my_graph->set( 
+	title => 'Non-numerical X axis',
+	x_label => 'Time (hours)',
+	y_label => 'Mass units',
+        skip_undef => 1,
+
+	x_tick_number => 'auto',
+	x_ticks     => 1,
+	x_tick_length => -4,
+
+	line_width => 2,
+	x_label_position => 1/2,
+	r_margin => 15,
+
+	transparent => 0,
+);
+
+$my_graph->set(legend_placement => 'RC');
+$my_graph->set_legend(qw(344.16 702.75 358.18 Sum));
+$my_graph->plot($data);
+save_chart($my_graph);
+
+1;