diff --git a/django/forms/models.py b/django/forms/models.py
index e292c1b9a73e3..430dd4d7ccee8 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -236,6 +236,8 @@ def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                  empty_permitted=False, instance=None):
         opts = self._meta
         if instance is None:
+            if opts.model is None:
+                raise ValueError('ModelForm has no model class specified.')
             # if we didn't get an instance, instantiate a new one
             self.instance = opts.model()
             object_data = {}
diff --git a/tests/regressiontests/model_forms_regress/tests.py b/tests/regressiontests/model_forms_regress/tests.py
index 3eeecb28e40f6..c923a12e15e4f 100644
--- a/tests/regressiontests/model_forms_regress/tests.py
+++ b/tests/regressiontests/model_forms_regress/tests.py
@@ -145,5 +145,10 @@ def test_string_message(self):
         data = {'name': 'anonymous'}
         form = RealPersonForm(data)
         self.assertEqual(form.is_valid(), False)
-        self.assertEqual(form.errors['__all__'], ['Please specify a real name.']) 
+        self.assertEqual(form.errors['__all__'], ['Please specify a real name.'])
 
+class ModelClassTests(TestCase):
+    def test_no_model_class(self):
+        class NoModelModelForm(forms.ModelForm):
+            pass
+        self.assertRaises(ValueError, NoModelModelForm)