diff --git a/dulwich/tests/test_repository.py b/dulwich/tests/test_repository.py
index 170fbecb3..7b424973d 100644
--- a/dulwich/tests/test_repository.py
+++ b/dulwich/tests/test_repository.py
@@ -777,4 +777,5 @@ def test_discover_isrepo(self):
         self.assertEqual(r.head(), self._repo.head())
 
     def test_discover_notrepo(self):
-        self.assertRaises(NotGitRepository, Repo.discover('/'))
+        with self.assertRaises(NotGitRepository):
+            Repo.discover('/')