diff --git a/_pytest/mark.py b/_pytest/mark.py
index ccc90d6e8..23ec44c29 100644
--- a/_pytest/mark.py
+++ b/_pytest/mark.py
@@ -229,7 +229,7 @@ def pytest_configure(config):
 
 
 def pytest_unconfigure(config):
-    MARK_GEN._config = config._old_mark_config
+    MARK_GEN._config = getattr(config, '_old_mark_config', None)
 
 
 class MarkGenerator(object):