diff --git a/convlab2/dst/dstc9/utils.py b/convlab2/dst/dstc9/utils.py
index ad10cf5a5e4450dddbc0dacdeecaed0be7b24767..9eee5f32eccad418259d278e3f08d4428e72fe0d 100644
--- a/convlab2/dst/dstc9/utils.py
+++ b/convlab2/dst/dstc9/utils.py
@@ -79,7 +79,7 @@ def unify_value(value, subtask):
         'crosswoz': {
             'None': '',
         }
-    }[subtask].get(value, value)
+    }[subtask].get(value, value).lower()
 
     return ' '.join(value.strip().split())