gistfile1.diff

diff --git a/django/db/models/base.py b/django/db/models/base.py
index c2f711e..dedfbee 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -1659,6 +1659,8 @@ def model_unpickle(model_id, attrs, factory):
     Used to unpickle Model subclasses with deferred fields.
     """
     if isinstance(model_id, tuple):
+        if not apps.ready:
+            apps.populate(settings.INSTALLED_APPS)
         model = apps.get_model(*model_id)
     else:
         # Backwards compat - the model was cached directly in earlier versions.