diff --git a/skimage/transform/tests/test_hough_transform.py b/skimage/transform/tests/test_hough_transform.py
index 0e6c6573..fce7013c 100644
--- a/skimage/transform/tests/test_hough_transform.py
+++ b/skimage/transform/tests/test_hough_transform.py
@@ -142,9 +142,9 @@ def test_hough_circle():
 
     out1 = tf.hough_circle(img, radius)
     out2 = tf.hough_circle(img, [radius])
-    assert_equal(out1,out2)
+    assert_equal(out1, out2)
     out = tf.hough_circle(img, np.array([radius], dtype=np.intp))
-    assert_equal(out,out1)
+    assert_equal(out, out1)
     x, y = np.where(out[0] == out[0].max())
     assert_equal(x[0], x_0)
     assert_equal(y[0], y_0)