diff --git a/fairseq/dataclass/utils.py b/fairseq/dataclass/utils.py
index 401c212ecc..a4d4a412dd 100644
--- a/fairseq/dataclass/utils.py
+++ b/fairseq/dataclass/utils.py
@@ -162,7 +162,7 @@ def get_kwargs_from_dc(
                     continue
                 else:
                     del kwargs["default"]
-            if delete_default:
+            if delete_default and "default" in kwargs:
                 del kwargs["default"]
         try:
             parser.add_argument(*field_args, **kwargs)