diff --git a/graphene-django/graphene_django/types.py b/graphene-django/graphene_django/types.py
index c975a550..df3257ad 100644
--- a/graphene-django/graphene_django/types.py
+++ b/graphene-django/graphene_django/types.py
@@ -90,7 +90,9 @@ class DjangoObjectType(six.with_metaclass(DjangoObjectTypeMeta, ObjectType)):
         if isinstance(root, cls):
             return True
         if not is_valid_django_model(type(root)):
-            raise Exception('Received incompatible instance "{}"'.format(root))
+            raise Exception((
+                'Received incompatible instance "{}".'
+            ).format(root))
         model = root._meta.model
         return model == cls._meta.model