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