diff --git a/tests/test_octodns_processor_filter.py b/tests/test_octodns_processor_filter.py
index 409ec50..6525900 100644
--- a/tests/test_octodns_processor_filter.py
+++ b/tests/test_octodns_processor_filter.py
@@ -194,6 +194,12 @@ class TestNetworkValueFilter(TestCase):
     ]:
         zone.add_record(record)
 
+    def test_bad_config(self):
+        with self.assertRaises(ValueError):
+            filter_private = NetworkValueRejectlistFilter(
+                'rejectlist', set(('string', '42.42.42.42/43'))
+            )
+
     def test_reject(self):
         filter_private = NetworkValueRejectlistFilter(
             'rejectlist', set(('10.0.0.0/8', 'fd00::/8'))