diff -r af388201c997 Lib/datetime.py
--- a/Lib/datetime.py	Tue Mar 22 18:48:50 2016 +0100
+++ b/Lib/datetime.py	Thu Mar 24 01:08:07 2016 -0400
@@ -1535,6 +1535,8 @@
                     tz = timezone(delta)
             else:
                 tz = timezone(timedelta(seconds=gmtoff), zone)
+                self.replace(tzinfo=tz)
+                return self
 
         elif not isinstance(tz, tzinfo):
             raise TypeError("tz argument must be an instance of tzinfo")
diff -r af388201c997 Lib/test/datetimetester.py
--- a/Lib/test/datetimetester.py	Tue Mar 22 18:48:50 2016 +0100
+++ b/Lib/test/datetimetester.py	Thu Mar 24 01:08:07 2016 -0400
@@ -3457,11 +3457,11 @@
         dt = self.theclass(2012, 11, 4, 6, 30, tzinfo=timezone.utc)
         local = dt.astimezone()
         self.assertEqual(dt, local)
-        self.assertEqual(local.strftime("%z %Z"), "-0500 EST")
+        self.assertEqual(local.strftime("%z %Z"), "+0000 UTC")
         dt = self.theclass(2012, 11, 4, 5, 30, tzinfo=timezone.utc)
         local = dt.astimezone()
         self.assertEqual(dt, local)
-        self.assertEqual(local.strftime("%z %Z"), "-0400 EDT")
+        self.assertEqual(local.strftime("%z %Z"), "+0000 UTC")
 
     def test_aware_subtract(self):
         cls = self.theclass