diff --git a/django/contrib/contenttypes/models.py b/django/contrib/contenttypes/models.py
index 1bb07e0..9ccadb0 100644
--- a/django/contrib/contenttypes/models.py
+++ b/django/contrib/contenttypes/models.py
@@ -17,9 +17,8 @@ def get_by_natural_key(self, app_label, model):
 
     def _get_opts(self, model):
         opts = model._meta
-        while opts.proxy:
-            model = opts.proxy_for_model
-            opts = model._meta
+        if model._deferred:
+            opts = model.__class__.__bases__[0]._meta
         return opts
 
     def _get_from_cache(self, opts):
diff --git a/tests/modeltests/proxy_models/tests.py b/tests/modeltests/proxy_models/tests.py
index 3ec8465..04ea203 100644
--- a/tests/modeltests/proxy_models/tests.py
+++ b/tests/modeltests/proxy_models/tests.py
@@ -217,8 +217,10 @@ def _handler(*args, **kwargs):
         signals.post_save.disconnect(h6, sender=MyPersonProxy)
 
     def test_content_type(self):
+        # A model and a proxy of this model do not
+        # share the same ContentType see #17648
         ctype = ContentType.objects.get_for_model
-        self.assertTrue(ctype(Person) is ctype(OtherPerson))
+        self.assertFalse(ctype(Person) is ctype(OtherPerson))
 
     def test_user_userproxy_userproxyproxy(self):
         User.objects.create(name='Bruce')
diff --git a/tests/regressiontests/defer_regress/tests.py b/tests/regressiontests/defer_regress/tests.py
index 4afe39b..4e4d80c 100644
--- a/tests/regressiontests/defer_regress/tests.py
+++ b/tests/regressiontests/defer_regress/tests.py
@@ -169,6 +169,14 @@ def test_only_and_defer_usage_on_proxy_models(self):
         self.assertEqual(dp.name, proxy.name, msg=msg)
         self.assertEqual(dp.value, proxy.value, msg=msg)
 
+        # Instances of proxy models with deferred fields should
+        # return the content type of the proxy model (bug #17648)
+        ctype = ContentType.objects.get_for_model
+        c1 = ctype(Proxy.objects.all()[0])
+        c2 = ctype(Proxy.objects.defer("name")[0])
+        c3 = ctype(Proxy.objects.only("name")[0])
+        self.assertTrue(c1 is c2 is c3)
+
     def test_resolve_columns(self):
         rt = ResolveThis.objects.create(num=5.0, name='Foobar')
         qs = ResolveThis.objects.defer('num')