diff --git a/ops/_private/timeconv.py b/ops/_private/timeconv.py
index c97c8051e..0774e3942 100644
--- a/ops/_private/timeconv.py
+++ b/ops/_private/timeconv.py
@@ -52,7 +52,9 @@ def parse_rfc3339(s: str) -> datetime.datetime:
 
     microsecond = round(float(sfrac or '0') * 1000000)
     carry, microsecond = divmod(microsecond, 1000000)
-    ss = int(ss) + carry
 
-    return datetime.datetime(int(y), int(m), int(d), int(hh), int(mm), ss,
-                             microsecond=microsecond, tzinfo=tz)
+    parsed = datetime.datetime(int(y), int(m), int(d), int(hh), int(mm), int(ss),
+                               microsecond=microsecond, tzinfo=tz)
+    if carry:
+        return parsed + datetime.timedelta(seconds=carry)
+    return parsed
diff --git a/test/test_private.py b/test/test_private.py
index b2099fe07..f7c816a1a 100644
--- a/test/test_private.py
+++ b/test/test_private.py
@@ -75,6 +75,9 @@ def test_parse_rfc3339(self):
         self.assertEqual(timeconv.parse_rfc3339('2006-08-28T13:20:00.99999999Z'),
                          datetime.datetime(2006, 8, 28, 13, 20, 1, 0, tzinfo=utc))
 
+        self.assertEqual(timeconv.parse_rfc3339('2006-12-31T23:59:59.99999999Z'),
+                         datetime.datetime(2007, 1, 1, 0, 0, 0, 0, tzinfo=utc))
+
         tzinfo = datetime.timezone(datetime.timedelta(hours=-11, minutes=-30))
         self.assertEqual(timeconv.parse_rfc3339('2020-12-25T13:45:50.123456789-11:30'),
                          datetime.datetime(2020, 12, 25, 13, 45, 50, 123457, tzinfo=tzinfo))