diff --git a/tests/unit/test_settings.py b/tests/unit/test_settings.py
index 99310a42c1..a3b62f8ee4 100644
--- a/tests/unit/test_settings.py
+++ b/tests/unit/test_settings.py
@@ -37,6 +37,8 @@ def test_smoothing_parameters(self):
             pybamm.settings.heaviside_smoothing = -10
         with self.assertRaisesRegex(ValueError, "positive number"):
             pybamm.settings.abs_smoothing = -10
+        with self.assertRaisesRegex(ValueError, "'soft', or 'smooth'"):
+            pybamm.settings.min_max_mode = "unknown"
         pybamm.settings.set_smoothing_parameters("exact")