diff --git a/htdocs/samples/axes_x_tick_rotate.html b/htdocs/samples/axes_x_tick_rotate.html
index c226455..2802232 100644
--- a/htdocs/samples/axes_x_tick_rotate.html
+++ b/htdocs/samples/axes_x_tick_rotate.html
@@ -20,7 +20,7 @@
           x: {
             tick: {
               format: function () { return "hogehogehogehogehoge"; },
-              rotate: 30,
+              rotate: -30,
             },
             label: {
               text: 'Hogehoge',
diff --git a/src/size.js b/src/size.js
index 2a91b26..52f46a4 100644
--- a/src/size.js
+++ b/src/size.js
@@ -105,11 +105,11 @@ c3_chart_internal_fn.getHorizontalAxisHeight = function (axisId) {
     if (axisId === 'y2' && !config.axis_y2_show) { return $$.rotated_padding_top; }
     // Calculate x axis height when tick rotated
     if (axisId === 'x' && !config.axis_rotated && config.axis_x_tick_rotate) {
-        h = 30 + $$.axis.getMaxTickWidth(axisId) * Math.cos(Math.PI * (90 - config.axis_x_tick_rotate) / 180);
+        h = 30 + $$.axis.getMaxTickWidth(axisId) * Math.cos(Math.PI * (90 - Math.abs(config.axis_x_tick_rotate)) / 180);
     }
     // Calculate y axis height when tick rotated
     if (axisId === 'y' && config.axis_rotated && config.axis_y_tick_rotate) {
-        h = 30 + $$.axis.getMaxTickWidth(axisId) * Math.cos(Math.PI * (90 - config.axis_y_tick_rotate) / 180);
+        h = 30 + $$.axis.getMaxTickWidth(axisId) * Math.cos(Math.PI * (90 - Math.abs(config.axis_y_tick_rotate)) / 180);
     }
     return h + ($$.axis.getLabelPositionById(axisId).isInner ? 0 : 10) + (axisId === 'y2' ? -10 : 0);
 };