diff --git a/contact_map/tests/test_contact_count.py b/contact_map/tests/test_contact_count.py
index ab87a89..1924ed7 100644
--- a/contact_map/tests/test_contact_count.py
+++ b/contact_map/tests/test_contact_count.py
@@ -62,10 +62,9 @@ def test_plot_kwargs(self):
     @pytest.mark.skipif(not HAS_MATPLOTLIB, reason="Missing matplotlib")
     def test_pixel_warning(self):
         # This should not raise a warning (5*2>=10)
-        with pytest.warns(None) as record:
+        with warnings.catch_warnings():
+            warnings.simplefilter('error')
             self.atom_contacts.plot(figsize=(5, 5), dpi=2)
-        # See if no warning was raised
-        assert len(record) == 0
 
         # Now raise the warning as 4*2 < 10
         with pytest.warns(RuntimeWarning) as record: