Index: django/db/models/loading.py
===================================================================
--- django/db/models/loading.py	(revision 10369)
+++ django/db/models/loading.py	(working copy)
@@ -80,7 +80,9 @@
                 # We will check again once all the recursion has finished (in
                 # populate).
                 self.postponed.append(app_name)
-            return None
+                return None
+            else:
+                raise
         self.nesting_level -= 1
         if models not in self.app_store:
             self.app_store[models] = len(self.app_store)