diff --git a/django_pandas/io.py b/django_pandas/io.py
index 8764594..2e3811f 100644
--- a/django_pandas/io.py
+++ b/django_pandas/io.py
@@ -200,7 +200,7 @@ def read_frame(qs, fieldnames=(), index_col=None, coerce_float=False,
         fields = qs.model._meta.fields
         fieldnames = [f.name for f in fields]
 
-    if not is_values_queryset(qs):
+    if not issubclass(qs._iterable_class, django.db.models.query.ValuesListIterable):
         qs = qs.values_list(*fieldnames)
     recs = qs.iterator()
 
diff --git a/django_pandas/tests/test_io.py b/django_pandas/tests/test_io.py
index 95434a2..07d3700 100644
--- a/django_pandas/tests/test_io.py
+++ b/django_pandas/tests/test_io.py
@@ -47,8 +47,7 @@ def test_basic(self):
         df1 = read_frame(qs, ['col1', 'col2'])
         self.assertEqual(df1.shape, (qs.count(), 2))
 
-    def test_compress_basic(self):
-        qs = MyModel.objects.all()
+    def assert_compress_basic(self, qs):
         df = read_frame(qs, compress=True)
 
         # Test automatic inference of dtypes
@@ -59,6 +58,14 @@ def test_compress_basic(self):
 
         # Compress should use less memory
         self.assertLess(df.memory_usage().sum(), read_frame(qs).memory_usage().sum())
+        # Uses qs.iterator() rather than for x in qs.
+        self.assertFalse(qs._result_cache)
+
+    def test_compress_basic(self):
+        qs = MyModel.objects.all()
+        self.assert_compress_basic(qs)
+        self.assert_compress_basic(qs.values())
+        self.assert_compress_basic(qs.values_list())
 
     def test_compress_bad_argument(self):
         qs = MyModel.objects.all()
@@ -103,6 +110,8 @@ def test_compress_custom_field(self):
         # Memory usage is ordered as df1 < df2 < read_frame(qs, compress=False)
         self.assertLess(df2.memory_usage().sum(), read_frame(qs).memory_usage().sum())
         self.assertLess(df1.memory_usage().sum(), df2.memory_usage().sum())
+        # Uses qs.iterator() rather than for x in qs.
+        self.assertFalse(qs._result_cache)
 
     def test_values(self):
         qs = MyModel.objects.all()