diff --git a/tests/test_core.py b/tests/test_core.py
index dd69a96..c666a3a 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -389,13 +389,23 @@ def test_unknown_preferredencoding_warned_and_fallback():
     """Ensure a locale without a codec emits a warning."""
     @as_subprocess
     def child():
+        warnings.filterwarnings("error", category=UserWarning)
+        match = ('LookupError: unknown encoding: ---unknown--encoding---, '
+                 'defaulting to UTF-8 for keyboard.')
         with mock.patch('locale.getpreferredencoding') as get_enc:
             get_enc.return_value = '---unknown--encoding---'
-            with pytest.warns(UserWarning, match=(
-                    'LookupError: unknown encoding: ---unknown--encoding---, '
-                    'defaulting to UTF-8 for keyboard.')):
-                t = TestTerminal()
-                assert t._encoding == 'UTF-8'
+            try:
+                TestTerminal()
+            except UserWarning as e:
+                assert match in str(e)
+            else:
+                raise AssertionError('Did not raise warning')
+
+            warnings.filterwarnings("ignore", category=UserWarning)
+            t = TestTerminal()
+            assert t._encoding == 'UTF-8'
+
+        warnings.resetwarnings()

     child()