diff --git a/tests/conftest.py b/tests/conftest.py
index cf93428595cf2955ec7c81925f5e5c5d241df52a..bb4ffc4a9e429a8e2c84de56f3487669840333fe 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -7,6 +7,8 @@ from . import testutil
 @pytest.fixture(scope='session', autouse=True)
 def clean_environment(tmpdir_factory):
     config_path_s = str(testutil.test_path('userconfig'))
+    for key in ['LANG', 'LANGUAGE', 'LC_ALL', 'LC_CTYPE', 'LC_MONETARY']:
+        os.environ[key] = 'en_US.UTF-8'
     os.environ.pop('RTAUTH', None)
     os.environ.pop('RTPASSWD', None)
     os.environ.pop('RTSERVER', None)