diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index ebd4ca6..bae6575 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -3,6 +3,7 @@ Next (tbd)
 
 * `#16 <https://github.com/pytest-dev/pytest-reportlog/issues/15>`_: switch recommended file extension to `jsonl <https://jsonlines.org/>`__.
 * `#17 <https://github.com/pytest-dev/pytest-reportlog/issues/17>`_: add compression support for ``.bz2``/``.gz``/``.xz`` log file extensions.
+* `#12 <https://github.com/pytest-dev/pytest-reportlog/issues/12>`_: handle unserializable objects with a pinpointed marker
 
 
 0.3.0 (2023-04-26)
diff --git a/src/pytest_reportlog/plugin.py b/src/pytest_reportlog/plugin.py
index ab9b9ec..b15a3d9 100644
--- a/src/pytest_reportlog/plugin.py
+++ b/src/pytest_reportlog/plugin.py
@@ -63,11 +63,7 @@ def close(self):
             self._file = None
 
     def _write_json_data(self, data):
-        try:
-            json_data = json.dumps(data)
-        except TypeError:
-            data = cleanup_unserializable(data)
-            json_data = json.dumps(data)
+        json_data = json.dumps(data, default=unserializable_to_marked_str)
         self._file.write(json_data + "\n")
         self._file.flush()
 
@@ -92,7 +88,7 @@ def pytest_warning_recorded(self, warning_message, when, nodeid, location):
             ),
             "filename": warning_message.filename,
             "lineno": warning_message.lineno,
-            "message": warning_message.message,
+            "message": str(warning_message.message),
         }
         extra_data = {
             "$report_type": "WarningMessage",
@@ -112,13 +108,6 @@ def pytest_terminal_summary(self, terminalreporter):
         terminalreporter.write_sep("-", f"generated report log file: {self._log_path}")
 
 
-def cleanup_unserializable(d: Dict[str, Any]) -> Dict[str, Any]:
-    """Return new dict with entries that are not json serializable by their str()."""
-    result = {}
-    for k, v in d.items():
-        try:
-            json.dumps({k: v})
-        except TypeError:
-            v = str(v)
-        result[k] = v
-    return result
+def unserializable_to_marked_str(obj: object) -> Dict[str, str]:
+    """for a object that json can not serialize. return {"$no-json": str(obj)}"""
+    return {"$no-json": str(obj)}
diff --git a/tests/test_reportlog.py b/tests/test_reportlog.py
index 72d3813..3198827 100644
--- a/tests/test_reportlog.py
+++ b/tests/test_reportlog.py
@@ -6,7 +6,7 @@
 from pathlib import Path
 from _pytest.reports import BaseReport
 
-from pytest_reportlog.plugin import cleanup_unserializable, _open_filtered_writer
+from pytest_reportlog.plugin import _open_filtered_writer, unserializable_to_marked_str
 
 from typing_extensions import Protocol, Literal
 
@@ -133,10 +133,11 @@ def test_warning():
     }
 
 
-def test_cleanup_unserializable():
+def test_unserializable_to_marked():
     """Unittest for the cleanup_unserializable function"""
+
     good = {"x": 1, "y": ["a", "b"]}
-    new = cleanup_unserializable(good)
+    new = json.loads(json.dumps(good, default=unserializable_to_marked_str))
     assert new == good
 
     class C:
@@ -144,5 +145,5 @@ def __str__(self):
             return "C instance"
 
     bad = {"x": 1, "y": ["a", "b"], "c": C()}
-    new = cleanup_unserializable(bad)
-    assert new == {"x": 1, "c": "C instance", "y": ["a", "b"]}
+    new_bad = json.loads(json.dumps(bad, default=unserializable_to_marked_str))
+    assert new_bad == {**bad, "c": {"$no-json": "C instance"}}