diff --git a/compliance_checker/tests/test_cf.py b/compliance_checker/tests/test_cf.py
index 5ae68f00..65088f84 100644
--- a/compliance_checker/tests/test_cf.py
+++ b/compliance_checker/tests/test_cf.py
@@ -1298,7 +1298,7 @@ def test_check_time_coordinate(self):
         dataset = MockTimeSeries()
         # NB: >= 60 seconds is nonstandard, but isn't actually a CF requirement
         # until CF 1.9 onwards
-        dataset.variables["time"].units = "months since 0-1-1 23:00:59"
+        dataset.variables["time"].units = "months since 0-1-1 23:00:60"
         dataset.variables["time"].climatology = (
             "nonexistent_variable_reference_only_used_to_test_year_zero_failure"
         )