diff --git a/tests/test_superresolution.py b/tests/test_superresolution.py
index 4df914acd0b552a425d2a046091a46cc92d229da..50f0ca9721fbd82ae5e199a77ecd47e565fa733b 100644
--- a/tests/test_superresolution.py
+++ b/tests/test_superresolution.py
@@ -120,8 +120,9 @@ def test_polar_inverted_transform():
                 (args.norm(), sympy.atan2(args[1]-x.shape[1]/2, args[0]-x.shape[0]/2) / sympy.pi * x.shape[1]/2))
 
         def inv():
-            return lambda l: sympy.Matrix((sympy.cos(l[1] * sympy.pi / x.shape[1]*2) * l[0],
-                                           sympy.sin(l[1] * sympy.pi / x.shape[1]*2) * l[0])) + sympy.Matrix(x.shape) * 0.5
+            return lambda l: (sympy.Matrix((sympy.cos(l[1] * sympy.pi / x.shape[1]*2) * l[0],
+                                            sympy.sin(l[1] * sympy.pi / x.shape[1]*2) * l[0]))
+                              + sympy.Matrix(x.shape) * 0.5)
 
     lenna_file = join(dirname(__file__), "test_data", "lenna.png")
     lenna = skimage.io.imread(lenna_file, as_gray=True).astype(np.float32)