diff --git a/skimage/draw/tests/test_draw3d.py b/skimage/draw/tests/test_draw3d.py
index 35925497..1d29e41e 100644
--- a/skimage/draw/tests/test_draw3d.py
+++ b/skimage/draw/tests/test_draw3d.py
@@ -5,17 +5,17 @@ from nose.tools import raises
 from skimage.draw import ellipsoid, ellipsoid_stats
 
 
-@raises('ValueError')
+@raises(ValueError)
 def test_ellipsoid_sign_paramters1():
     ellipsoid(-1, 2, 2)
 
 
-@raises('ValueError')
+@raises(ValueError)
 def test_ellipsoid_sign_paramters2():
     ellipsoid(0, 2, 2)
 
 
-@raises('ValueError')
+@raises(ValueError)
 def test_ellipsoid_sign_paramters3():
     ellipsoid(-3, -2, 2)