diff --git a/libs/langchain/langchain/evaluation/schema.py b/libs/langchain/langchain/evaluation/schema.py
index 3d664bf80b5..ba068c89b9e 100644
--- a/libs/langchain/langchain/evaluation/schema.py
+++ b/libs/langchain/langchain/evaluation/schema.py
@@ -120,10 +120,10 @@ class _EvalArgsMixin:
             ValueError: If the evaluator requires an input string but none is provided,
                 or if the evaluator requires a reference label but none is provided.
         """
-        if self.requires_input and input is None:
+        if self.requires_input and input_ is None:
             msg = f"{self.__class__.__name__} requires an input string."
             raise ValueError(msg)
-        if input is not None and not self.requires_input:
+        if input_ is not None and not self.requires_input:
             warn(self._skip_input_warning)
         if self.requires_reference and reference is None:
             msg = f"{self.__class__.__name__} requires a reference string."