diff --git a/flask_sqlalchemy/model.py b/flask_sqlalchemy/model.py
index 5e5ae797..43f76b95 100644
--- a/flask_sqlalchemy/model.py
+++ b/flask_sqlalchemy/model.py
@@ -118,5 +118,9 @@ class Model(object):
     query = None
 
     def __repr__(self):
-        pk = ', '.join(to_str(value) for value in inspect(self).identity)
+        identity = inspect(self).identity
+        if identity is None:
+            pk = "(transient {0})".format(id(self))
+        else:
+            pk = ', '.join(to_str(value) for value in identity)
         return '<{0} {1}>'.format(type(self).__name__, pk)
diff --git a/tests/test_model_class.py b/tests/test_model_class.py
index c64d8ad3..4e381bcc 100644
--- a/tests/test_model_class.py
+++ b/tests/test_model_class.py
@@ -43,6 +43,7 @@ class Report(db.Model):
     db.create_all()
 
     u = User(name='test')
+    assert repr(u).startswith("<User (transient ")
     db.session.add(u)
     db.session.flush()
     assert repr(u) == '<User test>'