diff --git a/skimage/feature/tests/test_canny.py b/skimage/feature/tests/test_canny.py
index 0bfb1fcf..17a147f3 100644
--- a/skimage/feature/tests/test_canny.py
+++ b/skimage/feature/tests/test_canny.py
@@ -70,26 +70,43 @@ class TestCanny(unittest.TestCase):
         result2 = F.canny(np.zeros((20, 20)), 4, 0, 0)
         self.assertTrue(np.all(result1 == result2))
 
+    def test_quantile_threshold(self):
+        image = img_as_float(data.camera()[::50,::50])
 
-def test_quantile_threshold():
-    image = img_as_float(data.camera()[::50,::50])
+        # Correct output produced manually with quantiles
+        # of 0.8 and 0.6 for high and low respectively
+        correct_output = np.array([[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+           [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+           [0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0],
+           [0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0],
+           [0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0],
+           [0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0],
+           [0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0],
+           [0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0],
+           [0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0],
+           [0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0],
+           [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]], dtype=bool)
 
-    # Correct output produced manually with quantiles
-    # of 0.8 and 0.6 for high and low respectively
-    correct_output = np.array([[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-       [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-       [0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0],
-       [0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0],
-       [0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0],
-       [0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0],
-       [0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0],
-       [0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0],
-       [0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0],
-       [0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0],
-       [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]], dtype=bool)
+        result = F.canny(image, low_threshold=0.6, high_threshold=0.8, quantile_threshold=True)
 
-    result = F.canny(image, low_threshold=0.6, high_threshold=0.8, quantile_threshold=True)
+        assert_equal(result, correct_output)
 
-    assert_equal(result, correct_output)
+    def test_invalid_quantile_threshold(self):
+        image = img_as_float(data.camera()[::50,::50])
 
+        with self.assertRaises(ValueError):
+            result = F.canny(image, quantile_threshold=True,
+                                low_threshold=0.5, high_threshold=3.6)
+
+        with self.assertRaises(ValueError):
+            result = F.canny(image, quantile_threshold=True,
+                                low_threshold=99, high_threshold=0.9)
+
+        with self.assertRaises(ValueError):
+            result = F.canny(image, quantile_threshold=True,
+                                low_threshold=-5, high_threshold=0.5)
+
+        with self.assertRaises(ValueError):
+            result = F.canny(image, quantile_threshold=True,
+                                low_threshold=0.5, high_threshold=-100)