diff --git a/fastNLP/core/metrics/element.py b/fastNLP/core/metrics/element.py
index 483e9a49..58fac838 100644
--- a/fastNLP/core/metrics/element.py
+++ b/fastNLP/core/metrics/element.py
@@ -75,6 +75,7 @@ class Element:
         return self._value
 
     def get_scalar(self) -> float:
+        self._check_value_initialized()
         return self.backend.get_scalar(self._value)
 
     def fill_value(self, value):