diff --git a/openapi_core/schema/schemas/exceptions.py b/openapi_core/schema/schemas/exceptions.py
index 2b87923..f325d18 100644
--- a/openapi_core/schema/schemas/exceptions.py
+++ b/openapi_core/schema/schemas/exceptions.py
@@ -48,13 +48,19 @@ class UnmarshalValueError(UnmarshalError):
 class InvalidSchemaValue(ValidateError):
     value = attr.ib()
     type = attr.ib()
-    schema_errors = attr.ib()
+    _schema_errors = attr.ib(default=None)
+    _schema_errors_iter = attr.ib(factory=list)
+
+    @property
+    def schema_errors(self):
+        if self._schema_errors is None:
+            self._schema_errors = list(self._schema_errors_iter)
+        return self._schema_errors
 
     def __str__(self):
-        errors = list(self.schema_errors)
         return (
             "Value {value} not valid for schema of type {type}: {errors}"
-        ).format(value=self.value, type=self.type, errors=errors)
+        ).format(value=self.value, type=self.type, errors=self.schema_errors)
 
 
 class UnmarshallerError(UnmarshalError):
diff --git a/openapi_core/schema/schemas/models.py b/openapi_core/schema/schemas/models.py
index 534c7b7..6869cc7 100644
--- a/openapi_core/schema/schemas/models.py
+++ b/openapi_core/schema/schemas/models.py
@@ -194,7 +194,8 @@ class Schema(object):
             return validator.validate(value)
         except ValidationError:
             errors_iter = validator.iter_errors(value)
-            raise InvalidSchemaValue(value, self.type, errors_iter)
+            raise InvalidSchemaValue(
+                value, self.type, schema_errors_iter=errors_iter)
 
     def unmarshal(self, value, custom_formatters=None, strict=True):
         """Unmarshal parameter from the value."""
diff --git a/tests/integration/validation/test_petstore.py b/tests/integration/validation/test_petstore.py
index 38ab8ba..f2ecaee 100644
--- a/tests/integration/validation/test_petstore.py
+++ b/tests/integration/validation/test_petstore.py
@@ -175,13 +175,14 @@ class TestPetstore(object):
 
         response_result = response_validator.validate(request, response)
 
-        errors = response_result.errors[0].original_exception.schema_errors
+        original_exc = response_result.errors[0].original_exception
         assert response_result.errors == [
             InvalidMediaTypeValue(
                 original_exception=InvalidSchemaValue(
                     type=SchemaType.OBJECT,
                     value=data_json,
-                    schema_errors=errors,
+                    schema_errors=original_exc.schema_errors,
+                    schema_errors_iter=original_exc._schema_errors_iter,
                 ),
             ),
         ]