diff --git a/tempest/test.py b/tempest/test.py
index ccb985a..ca626da 100644
--- a/tempest/test.py
+++ b/tempest/test.py
@@ -141,7 +141,7 @@
 
     @classmethod
     def tearDownClass(cls):
-        at_exit_set.remove(cls)
+        at_exit_set.discard(cls)
         if hasattr(super(BaseTestCase, cls), 'tearDownClass'):
             super(BaseTestCase, cls).tearDownClass()