diff -r 499e44b9bc66 Lib/datetime.py
--- a/Lib/datetime.py	Fri Sep 04 10:48:31 2015 +0200
+++ b/Lib/datetime.py	Fri Sep 04 10:50:07 2015 +0200
@@ -1362,13 +1362,12 @@ class datetime(date):
 
         A timezone info object may be passed in as well.
         """
-
         _check_tzinfo_arg(tz)
 
         converter = _time.localtime if tz is None else _time.gmtime
 
         t, frac = divmod(t, 1.0)
-        us = int(frac * 1e6)
+        us = _round_half_up(frac * 1e6)
 
         # If timestamp is less than one microsecond smaller than a
         # full second, us can be rounded up to 1000000.  In this case,
@@ -1386,9 +1385,9 @@ class datetime(date):
 
     @classmethod
     def utcfromtimestamp(cls, t):
-        "Construct a UTC datetime from a POSIX timestamp (like time.time())."
+        """Construct a naive UTC datetime from a POSIX timestamp."""
         t, frac = divmod(t, 1.0)
-        us = int(frac * 1e6)
+        us = _round_half_up(frac * 1e6)
 
         # If timestamp is less than one microsecond smaller than a
         # full second, us can be rounded up to 1000000.  In this case,
diff -r 499e44b9bc66 Lib/test/datetimetester.py
--- a/Lib/test/datetimetester.py	Fri Sep 04 10:48:31 2015 +0200
+++ b/Lib/test/datetimetester.py	Fri Sep 04 10:50:07 2015 +0200
@@ -1830,6 +1830,7 @@ class TestDateTime(TestDate):
             zero = fts(0)
             self.assertEqual(zero.second, 0)
             self.assertEqual(zero.microsecond, 0)
+            one = fts(1e-6)
             try:
                 minus_one = fts(-1e-6)
             except OSError:
@@ -1840,22 +1841,22 @@ class TestDateTime(TestDate):
                 self.assertEqual(minus_one.microsecond, 999999)
 
                 t = fts(-1e-8)
-                self.assertEqual(t, minus_one)
+                self.assertEqual(t, zero)
                 t = fts(-9e-7)
                 self.assertEqual(t, minus_one)
                 t = fts(-1e-7)
-                self.assertEqual(t, minus_one)
+                self.assertEqual(t, zero)
 
             t = fts(1e-7)
             self.assertEqual(t, zero)
             t = fts(9e-7)
-            self.assertEqual(t, zero)
+            self.assertEqual(t, one)
             t = fts(0.99999949)
             self.assertEqual(t.second, 0)
             self.assertEqual(t.microsecond, 999999)
             t = fts(0.9999999)
-            self.assertEqual(t.second, 0)
-            self.assertEqual(t.microsecond, 999999)
+            self.assertEqual(t.second, 1)
+            self.assertEqual(t.microsecond, 0)
 
     def test_insane_fromtimestamp(self):
         # It's possible that some platform maps time_t to double,
diff -r 499e44b9bc66 Modules/_datetimemodule.c
--- a/Modules/_datetimemodule.c	Fri Sep 04 10:48:31 2015 +0200
+++ b/Modules/_datetimemodule.c	Fri Sep 04 10:50:07 2015 +0200
@@ -4107,7 +4107,8 @@ datetime_from_timestamp(PyObject *cls, T
     time_t timet;
     long us;
 
-    if (_PyTime_ObjectToTimeval(timestamp, &timet, &us, _PyTime_ROUND_DOWN) == -1)
+    if (_PyTime_ObjectToTimeval(timestamp,
+                                &timet, &us, _PyTime_ROUND_HALF_UP) == -1)
         return NULL;
     return datetime_from_timet_and_us(cls, f, timet, (int)us, tzinfo);
 }