diff --git a/awslambdaric/lambda_runtime_marshaller.py b/awslambdaric/lambda_runtime_marshaller.py
index b591e69..42ee127 100644
--- a/awslambdaric/lambda_runtime_marshaller.py
+++ b/awslambdaric/lambda_runtime_marshaller.py
@@ -4,7 +4,7 @@
 
 import decimal
 import math
-
+import os
 import simplejson as json
 
 from .lambda_runtime_exception import FaultException
@@ -15,7 +15,10 @@
 # We also set 'ensure_ascii=False' so that the encoded json contains unicode characters instead of unicode escape sequences
 class Encoder(json.JSONEncoder):
     def __init__(self):
-        super().__init__(use_decimal=False, ensure_ascii=False)
+        if os.environ.get("AWS_EXECUTION_ENV") == "AWS_Lambda_python3.12":
+            super().__init__(use_decimal=False, ensure_ascii=False)
+        else:
+            super().__init__(use_decimal=False)
 
     def default(self, obj):
         if isinstance(obj, decimal.Decimal):
diff --git a/requirements/dev.txt b/requirements/dev.txt
index c432413..68377ce 100644
--- a/requirements/dev.txt
+++ b/requirements/dev.txt
@@ -9,3 +9,4 @@ bandit>=1.6.2
 # Test requirements
 pytest>=3.0.7
 mock>=2.0.0
+parameterized>=0.9.0
\ No newline at end of file
diff --git a/tests/test_lambda_runtime_marshaller.py b/tests/test_lambda_runtime_marshaller.py
index eb8b848..7cd73b4 100644
--- a/tests/test_lambda_runtime_marshaller.py
+++ b/tests/test_lambda_runtime_marshaller.py
@@ -3,12 +3,35 @@
 """
 
 import decimal
+import os
 import unittest
-
+from parameterized import parameterized
 from awslambdaric.lambda_runtime_marshaller import to_json
 
 
 class TestLambdaRuntimeMarshaller(unittest.TestCase):
+    execution_envs = (
+        "AWS_Lambda_python3.12",
+        "AWS_Lambda_python3.11",
+        "AWS_Lambda_python3.10",
+        "AWS_Lambda_python3.9",
+    )
+
+    envs_lambda_marshaller_ensure_ascii_false = {"AWS_Lambda_python3.12"}
+
+    execution_envs_lambda_marshaller_ensure_ascii_true = tuple(
+        set(execution_envs).difference(envs_lambda_marshaller_ensure_ascii_false)
+    )
+    execution_envs_lambda_marshaller_ensure_ascii_false = tuple(
+        envs_lambda_marshaller_ensure_ascii_false
+    )
+
+    def setUp(self):
+        self.org_os_environ = os.environ
+
+    def tearDown(self):
+        os.environ = self.org_os_environ
+
     def test_to_json_decimal_encoding(self):
         response = to_json({"pi": decimal.Decimal("3.14159")})
         self.assertEqual('{"pi": 3.14159}', response)
@@ -38,10 +61,22 @@ def test_json_serializer_is_not_default_json(self):
         self.assertFalse(hasattr(stock_json, "YOLO"))
         self.assertTrue(hasattr(simplejson, "YOLO"))
 
-    def test_to_json_unicode_encoding(self):
+    @parameterized.expand(execution_envs_lambda_marshaller_ensure_ascii_false)
+    def test_to_json_unicode_not_escaped_encoding(self, execution_env):
+        os.environ = {"AWS_EXECUTION_ENV": execution_env}
         response = to_json({"price": "£1.00"})
         self.assertEqual('{"price": "£1.00"}', response)
         self.assertNotEqual('{"price": "\\u00a31.00"}', response)
         self.assertEqual(
             19, len(response.encode("utf-8"))
         )  # would be 23 bytes if a unicode escape was returned
+
+    @parameterized.expand(execution_envs_lambda_marshaller_ensure_ascii_true)
+    def test_to_json_unicode_is_escaped_encoding(self, execution_env):
+        os.environ = {"AWS_EXECUTION_ENV": execution_env}
+        response = to_json({"price": "£1.00"})
+        self.assertEqual('{"price": "\\u00a31.00"}', response)
+        self.assertNotEqual('{"price": "£1.00"}', response)
+        self.assertEqual(
+            23, len(response.encode("utf-8"))
+        )  # would be 19 bytes if a escaped was returned