diff --git a/libs/langchain/langchain/output_parsers/boolean.py b/libs/langchain/langchain/output_parsers/boolean.py
index d670d155a34..c9e6dc615b1 100644
--- a/libs/langchain/langchain/output_parsers/boolean.py
+++ b/libs/langchain/langchain/output_parsers/boolean.py
@@ -19,13 +19,24 @@ class BooleanOutputParser(BaseOutputParser[bool]):
             boolean
 
         """
-        cleaned_text = text.strip()
-        if cleaned_text.upper() not in (self.true_val.upper(), self.false_val.upper()):
+        cleaned_upper_text = text.strip().upper()
+        if (
+            self.true_val.upper() in cleaned_upper_text
+            and self.false_val.upper() in cleaned_upper_text
+        ):
             raise ValueError(
-                f"BooleanOutputParser expected output value to either be "
-                f"{self.true_val} or {self.false_val}. Received {cleaned_text}."
+                f"Ambiguous response. Both {self.true_val} and {self.false_val} in "
+                f"received: {text}."
+            )
+        elif self.true_val.upper() in cleaned_upper_text:
+            return True
+        elif self.false_val.upper() in cleaned_upper_text:
+            return False
+        else:
+            raise ValueError(
+                f"BooleanOutputParser expected output value to include either "
+                f"{self.true_val} or {self.false_val}. Received {text}."
             )
-        return cleaned_text.upper() == self.true_val.upper()
 
     @property
     def _type(self) -> str:
diff --git a/libs/langchain/tests/unit_tests/output_parsers/test_boolean_parser.py b/libs/langchain/tests/unit_tests/output_parsers/test_boolean_parser.py
index 8804c36338e..60cad855be6 100644
--- a/libs/langchain/tests/unit_tests/output_parsers/test_boolean_parser.py
+++ b/libs/langchain/tests/unit_tests/output_parsers/test_boolean_parser.py
@@ -20,6 +20,17 @@ def test_boolean_output_parser_parse() -> None:
     result = parser.parse("no")
     assert result is False
 
+    # Test valid input
+    result = parser.parse("Not relevant (NO)")
+    assert result is False
+
+    # Test ambiguous input
+    try:
+        parser.parse("yes and no")
+        assert False, "Should have raised ValueError"
+    except ValueError:
+        pass
+
     # Test invalid input
     try:
         parser.parse("INVALID")