Fixed #19362 -- Detected invalid use of @python_2_unicode_compatible.

Thanks m3wolf for the report and akaariai for reproducing the problem.

1 files changed, 5 insertions, 0 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index a1f9e2f26e..bf9854d289 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -416,6 +416,11 @@ class Model(six.with_metaclass(ModelBase, object)):
 
     def __str__(self):
         if not six.PY3 and hasattr(self, '__unicode__'):
+            if type(self).__unicode__ == Model.__str__:
+                klass_name = type(self).__name__
+                raise RuntimeError("%s.__unicode__ is aliased to __str__. Did"
+                                   " you apply @python_2_unicode_compatible"
+                                   " without defining __str__?" % klass_name)
             return force_text(self).encode('utf-8')
         return '%s object' % self.__class__.__name__