diff --git a/convlab/evaluator/multiwoz_eval.py b/convlab/evaluator/multiwoz_eval.py
index 34984942fa0d9e87857042a6dc3d04d15967da9c..390ad3ce2bfb9d2e1648028b49bdffb5bd475f45 100755
--- a/convlab/evaluator/multiwoz_eval.py
+++ b/convlab/evaluator/multiwoz_eval.py
@@ -164,7 +164,7 @@ class MultiWozEvaluator(Evaluator):
 
         new_acts = list()
         for intent, domain, slot, value in da_turn:
-            if intent.lower() == 'book':
+            if intent.lower() == 'book' and not value:
                 ref = [_value for _intent, _domain, _slot, _value in da_turn if _domain ==
                        domain and _intent.lower() == 'inform' and _slot.lower() == 'ref']
                 ref = ref[0] if ref else ''