diff --git a/Lib/datetime.py b/Lib/datetime.py
index e4d7161..a15c6b0 100644
--- a/Lib/datetime.py
+++ b/Lib/datetime.py
@@ -1510,13 +1510,13 @@
                 # implied by tm_isdst.
                 delta = local - datetime(*_time.gmtime(ts)[:6])
                 dst = _time.daylight and localtm.tm_isdst > 0
-                gmtoff = _time.altzone if dst else _time.timezone
-                if delta == timedelta(seconds=-gmtoff):
+                gmtoff = -(_time.altzone if dst else _time.timezone)
+                if delta == timedelta(seconds=gmtoff):
                     tz = timezone(delta, _time.tzname[dst])
                 else:
                     tz = timezone(delta)
             else:
-                tz = timezone(timedelta(seconds=-gmtoff), zone)
+                tz = timezone(timedelta(seconds=gmtoff), zone)
 
         elif not isinstance(tz, tzinfo):
             raise TypeError("tz argument must be an instance of tzinfo")
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 4181d4f..a417170 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -3278,16 +3278,18 @@
         self.assertEqual(dt.astimezone(None), dt)
         self.assertEqual(dt.astimezone(), dt)
 
+    # Note that offset in TZ variable has the opposite sign to that
+    # produced by %z directive.
     @support.run_with_tz('EST+05EDT,M3.2.0,M11.1.0')
     def test_astimezone_default_eastern(self):
         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"), "-0500 EST")
         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"), "-0400 EDT")
 
     def test_aware_subtract(self):
         cls = self.theclass