diff --git a/autoconf/directory_config.py b/autoconf/directory_config.py
index b733b5f..39ebde7 100644
--- a/autoconf/directory_config.py
+++ b/autoconf/directory_config.py
@@ -80,6 +80,8 @@ def _getitem(self, item):
         return value
 
     def keys(self):
+        if not isinstance(self._dict, dict):
+            return iter(())
         return self._dict.keys()