diff --git a/MySQLdb/times.py b/MySQLdb/times.py
index 8a3c12d..5b7703f 100644
--- a/MySQLdb/times.py
+++ b/MySQLdb/times.py
@@ -64,7 +64,7 @@ def DateTime_or_None(s):
             ms = 0
         return datetime(*[ int(x) for x in d.split('-')+t.split(':')+[ms] ])
     except (SystemExit, KeyboardInterrupt):
-        raise
+        raise  # pragma: no cover
     except:
         return Date_or_None(s)
 
@@ -129,6 +129,6 @@ def mysql_timestamp_converter(s):
     try:
         return Timestamp(*parts)
     except (SystemExit, KeyboardInterrupt):
-        raise
+        raise  # pragma: no cover
     except:
         return None
diff --git a/tests/test_MySQLdb_times.py b/tests/test_MySQLdb_times.py
index f39951a..a172a9f 100644
--- a/tests/test_MySQLdb_times.py
+++ b/tests/test_MySQLdb_times.py
@@ -46,6 +46,7 @@ class TestX_or_None(unittest.TestCase):
         assert times.DateTime_or_None('2015-12-13T01:02:03.123456789') is None
 
     def test_timedelta_or_none(self):
+        assert times.TimeDelta_or_None('-1:0:0') == timedelta(0, -3600)
         assert times.TimeDelta_or_None('1:0:0') == timedelta(0, 3600)
         assert times.TimeDelta_or_None('12:55:30') == timedelta(0, 46530)
         assert times.TimeDelta_or_None('12:55:30.123456') == timedelta(0, 46530, 123456)