diff --git a/extra_foam/gui/plot_widgets/tests/test_plot_items.py b/extra_foam/gui/plot_widgets/tests/test_plot_items.py
index 90ba13d2..a58890a0 100644
--- a/extra_foam/gui/plot_widgets/tests/test_plot_items.py
+++ b/extra_foam/gui/plot_widgets/tests/test_plot_items.py
@@ -92,15 +92,16 @@ def testCurvePlotItem(self, dtype):
             item.setData(np.arange(2).astype(dtype), np.arange(3).astype(dtype))
 
         # test log mode
+        plot_bottom_right = np.log10(float(x[-1]))
         self._widget._plot_area._onLogXChanged(True)
         if dtype == float:
             _display()
-        assert item.boundingRect() == QRectF(0, 0, 1.0, 13.5)
+        assert item.boundingRect() == QRectF(0, 0, plot_bottom_right, 13.5)
         self._widget._plot_area._onLogYChanged(True)
         if dtype == float:
             _display()
         assert item.boundingRect().topLeft() == QPointF(0, 0)
-        assert item.boundingRect().bottomRight().x() == 1.0
+        assert item.boundingRect().bottomRight().x() == plot_bottom_right
         assert 1.2 > item.boundingRect().bottomRight().y() > 1.1
 
         # clear data
diff --git a/extra_foam/gui/pyqtgraph/graphicsItems/GraphicsObject.py b/extra_foam/gui/pyqtgraph/graphicsItems/GraphicsObject.py
index 03d949f3..7bca380a 100644
--- a/extra_foam/gui/pyqtgraph/graphicsItems/GraphicsObject.py
+++ b/extra_foam/gui/pyqtgraph/graphicsItems/GraphicsObject.py
@@ -129,7 +129,7 @@ def toLogScale(arr, policy=None):
         """Convert array result to logarithmic scale."""
         ret = np.nan_to_num(arr)
         ret[ret < 0] = 0
-        return np.log10(ret + 1)
+        return np.log10(ret, where=(ret > 0))
 
     def name(self):
         """An identity of the PlotItem.