diff --git a/tests/test_outline_painter.py b/tests/test_outline_painter.py
index 31c1f9c..6d6850b 100644
--- a/tests/test_outline_painter.py
+++ b/tests/test_outline_painter.py
@@ -323,7 +323,7 @@ def test_colours(self, p, opd):
             ((1.0, 0.0, 0.0, 1.0), 0.1, [(0.0, 0.0), (1.0, 0.0)]),
             ((0.0, 1.0, 0.0, 1.0), 0.1, [(0.0, 1.0), (1.0, 1.0)]),
             ((0.0, 0.0, 1.0, 1.0), 0.1, [(0.0, 2.0), (1.0, 2.0)]),
-            ((0.0, 0.0, 0.0, 128/255.), 0.1, [(0.0, 3.0), (1.0, 3.0)]),
+            ((0.0, 0.0, 0.0, pytest.approx(128/255.)), 0.1, [(0.0, 3.0), (1.0, 3.0)]),
             (None, 0.1, [(0.0, 4.0), (1.0, 4.0)]),
         ]