diff --git a/google/cloud/logging_v2/handlers/handlers.py b/google/cloud/logging_v2/handlers/handlers.py
index f6fa90d71..28960ae71 100644
--- a/google/cloud/logging_v2/handlers/handlers.py
+++ b/google/cloud/logging_v2/handlers/handlers.py
@@ -252,6 +252,7 @@ def _format_and_parse_message(record, formatter_handler):
         pass
     # if json_fields was set, create a dictionary using that
     if passed_json_fields and isinstance(passed_json_fields, collections.abc.Mapping):
+        passed_json_fields = passed_json_fields.copy()
         if message != "None":
             passed_json_fields["message"] = message
         return passed_json_fields
diff --git a/tests/unit/handlers/test_handlers.py b/tests/unit/handlers/test_handlers.py
index ad70061a6..1e431f1aa 100644
--- a/tests/unit/handlers/test_handlers.py
+++ b/tests/unit/handlers/test_handlers.py
@@ -846,6 +846,24 @@ def test_json_fields_with_json_message(self):
         self.assertEqual(result["key_m"], message["key_m"])
         self.assertEqual(result["key_j"], json_fields["key_j"])
 
+    def test_json_fields_input_unmodified(self):
+        # Related issue: https://github.com/googleapis/python-logging/issues/652
+        from google.cloud.logging_v2.handlers.handlers import _format_and_parse_message
+
+        message = "hello world"
+        json_fields = {"hello": "world"}
+        json_fields_orig = json_fields.copy()
+        record = logging.LogRecord("logname", None, None, None, message, None, None)
+        setattr(record, "json_fields", json_fields)
+        handler = logging.StreamHandler()
+        _format_and_parse_message(record, handler)
+        # ensure json_fields has no side-effects
+        self.assertEqual(set(json_fields.keys()), set(json_fields_orig.keys()))
+        for (key, value) in json_fields_orig.items():
+            self.assertEqual(
+                value, json_fields[key], f"expected_payload[{key}] != result[{key}]"
+            )
+
 
 class TestSetupLogging(unittest.TestCase):
     def _call_fut(self, handler, excludes=None):
diff --git a/tests/unit/handlers/test_structured_log.py b/tests/unit/handlers/test_structured_log.py
index 3fe322fe3..61bf36f65 100644
--- a/tests/unit/handlers/test_structured_log.py
+++ b/tests/unit/handlers/test_structured_log.py
@@ -511,6 +511,36 @@ def test_format_with_nested_json(self):
         result = json.loads(handler.format(record))
         self.assertEqual(result["outer"], json_fields["outer"])
 
+    def test_json_fields_input_unmodified(self):
+        # Related issue: https://github.com/googleapis/python-logging/issues/652
+        import logging
+
+        handler = self._make_one()
+        message = "hello world"
+        json_fields = {
+            "hello": "world",
+        }
+        json_fields_orig = json_fields.copy()
+        record = logging.LogRecord(
+            None,
+            logging.INFO,
+            None,
+            None,
+            message,
+            None,
+            None,
+        )
+        record.created = None
+        setattr(record, "json_fields", json_fields)
+        handler.filter(record)
+        handler.format(record)
+        # ensure json_fields has no side-effects
+        self.assertEqual(set(json_fields.keys()), set(json_fields_orig.keys()))
+        for (key, value) in json_fields_orig.items():
+            self.assertEqual(
+                value, json_fields[key], f"expected_payload[{key}] != result[{key}]"
+            )
+
     def test_emits_instrumentation_info(self):
         import logging
         import mock