diff --git a/Tests/test_core_resources.py b/Tests/test_core_resources.py
index 11f26d38e..fd8fb4244 100644
--- a/Tests/test_core_resources.py
+++ b/Tests/test_core_resources.py
@@ -179,3 +179,7 @@ class TestEnvVars(PillowTestCase):
         self.assert_warning(
             UserWarning, Image._apply_env_variables,
             {'PILLOW_BLOCKS_MAX': 'wat'})
+
+
+if __name__ == '__main__':
+    unittest.main()