Index: Lib/doctest.py
===================================================================
--- Lib/doctest.py	(revision 67009)
+++ Lib/doctest.py	(working copy)
@@ -961,7 +961,7 @@
         if module is None:
             filename = None
         else:
-            filename = getattr(module, '__file__', module.__name__)
+            filename = getattr(module, '__file__', None) or module.__name__
             if filename[-4:] in (".pyc", ".pyo"):
                 filename = filename[:-1]
         return self._parser.get_doctest(docstring, globs, name,