diff --git a/django/utils/timezone.py b/django/utils/timezone.py
index 9c70a11a7d..8138767fb2 100644
--- a/django/utils/timezone.py
+++ b/django/utils/timezone.py
@@ -351,6 +351,8 @@ def make_aware(value, timezone):
     """
     Makes a naive datetime.datetime in a given time zone aware.
     """
+    if is_aware(value):
+        raise ValueError("make_aware expects a naive value, got %s" % value)
     if hasattr(timezone, 'localize'):
         # available for pytz time zones
         return timezone.localize(value, is_dst=None)
@@ -363,6 +365,8 @@ def make_naive(value, timezone):
     """
     Makes an aware datetime.datetime naive in a given time zone.
     """
+    if is_naive(value):
+        raise ValueError("make_naive expects an aware value, got %s" % value)
     value = value.astimezone(timezone)
     if hasattr(timezone, 'normalize'):
         # available for pytz time zones
diff --git a/tests/utils_tests/test_timezone.py b/tests/utils_tests/test_timezone.py
index 1d608d0951..4b5a39a928 100644
--- a/tests/utils_tests/test_timezone.py
+++ b/tests/utils_tests/test_timezone.py
@@ -71,3 +71,28 @@ class TimezoneTests(unittest.TestCase):
     def test_pickling_unpickling(self):
         self.assertIsInstance(pickle.loads(pickle.dumps(timezone.UTC())), timezone.UTC)
         self.assertIsInstance(pickle.loads(pickle.dumps(timezone.LocalTimezone())), timezone.LocalTimezone)
+
+    def test_is_aware(self):
+        self.assertTrue(timezone.is_aware(datetime.datetime(2011, 9, 1, 13, 20, 30, tzinfo=EAT)))
+        self.assertFalse(timezone.is_aware(datetime.datetime(2011, 9, 1, 13, 20, 30)))
+
+    def test_is_naive(self):
+        self.assertFalse(timezone.is_naive(datetime.datetime(2011, 9, 1, 13, 20, 30, tzinfo=EAT)))
+        self.assertTrue(timezone.is_naive(datetime.datetime(2011, 9, 1, 13, 20, 30)))
+
+    def test_make_aware(self):
+        self.assertEqual(
+            timezone.make_aware(datetime.datetime(2011, 9, 1, 13, 20, 30), EAT),
+            datetime.datetime(2011, 9, 1, 13, 20, 30, tzinfo=EAT))
+        with self.assertRaises(ValueError):
+            timezone.make_aware(datetime.datetime(2011, 9, 1, 13, 20, 30, tzinfo=EAT), EAT)
+
+    def test_make_naive(self):
+        self.assertEqual(
+            timezone.make_naive(datetime.datetime(2011, 9, 1, 13, 20, 30, tzinfo=EAT), EAT),
+            datetime.datetime(2011, 9, 1, 13, 20, 30))
+        self.assertEqual(
+            timezone.make_naive(datetime.datetime(2011, 9, 1, 17, 20, 30, tzinfo=ICT), EAT),
+            datetime.datetime(2011, 9, 1, 13, 20, 30))
+        with self.assertRaises(ValueError):
+            timezone.make_naive(datetime.datetime(2011, 9, 1, 13, 20, 30), EAT)