diff --git a/tests/test_validation.py b/tests/test_validation.py
index cc6d29a23..d39a4618e 100644
--- a/tests/test_validation.py
+++ b/tests/test_validation.py
@@ -305,3 +305,11 @@ class ValidationTest(unittest.TestCase):
         )
 
         validate_config(cfg)
+
+        cfg = DictDefault(
+            {
+                "optimizer": "adafactor",
+            }
+        )
+
+        validate_config(cfg)