diff --git a/openapi_core/unmarshalling/schemas/exceptions.py b/openapi_core/unmarshalling/schemas/exceptions.py
index 43aaa2e2..8096fb64 100644
--- a/openapi_core/unmarshalling/schemas/exceptions.py
+++ b/openapi_core/unmarshalling/schemas/exceptions.py
@@ -20,7 +20,7 @@ class FormatterNotFoundError(UnmarshallerError):
     def __str__(self) -> str:
         return f"Formatter not found for {self.type_format} format"
 
-
+@dataclass
 class FormatUnmarshalError(UnmarshallerError):
     """Unable to unmarshal value for format"""