diff --git a/mvt/common/encoding.py b/mvt/common/encoding.py
new file mode 100644
index 0000000..c96d56f
--- /dev/null
+++ b/mvt/common/encoding.py
@@ -0,0 +1,27 @@
+import json
+
+
+class CustomJSONEncoder(json.JSONEncoder):
+    """
+    Custom JSON encoder to handle non-standard types.
+
+    Some modules are storing non-UTF-8 bytes in their results dictionaries.
+    This causes exceptions when the results are being encoded as JSON.
+
+    Of course this means that when MVT is run via `check-iocs` with existing
+    results, the encoded version will be loaded back into the dictionary.
+    Modules should ensure they encode anything that needs to be compared
+    against an indicator in a JSON-friendly type.
+    """
+
+    def default(self, o):
+        if isinstance(o, bytes):
+            # If it's utf-8, try and use that first
+            try:
+                return o.decode("utf-8")
+            except UnicodeError:
+                # Otherwise use a hex representation for any byte type
+                return "0x" + o.hex()
+
+        # For all other types try to use the string representation.
+        return str(o)
diff --git a/mvt/common/module.py b/mvt/common/module.py
index b7a63fc..55d54f3 100644
--- a/mvt/common/module.py
+++ b/mvt/common/module.py
@@ -4,13 +4,13 @@
 #   https://license.mvt.re/1.1/
 
 import csv
+import json
 import logging
 import os
 import re
 from typing import Any, Dict, List, Optional, Union
 
-import simplejson as json
-
+from .encoding import CustomJSONEncoder
 from .utils import exec_or_profile
 
 
@@ -103,7 +103,7 @@ class MVTModule:
             results_json_path = os.path.join(self.results_path, results_file_name)
             with open(results_json_path, "w", encoding="utf-8") as handle:
                 try:
-                    json.dump(self.results, handle, indent=4, default=str)
+                    json.dump(self.results, handle, indent=4, cls=CustomJSONEncoder)
                 except Exception as exc:
                     self.log.error(
                         "Unable to store results of module %s to file %s: %s",
@@ -116,7 +116,7 @@ class MVTModule:
             detected_file_name = f"{name}_detected.json"
             detected_json_path = os.path.join(self.results_path, detected_file_name)
             with open(detected_json_path, "w", encoding="utf-8") as handle:
-                json.dump(self.detected, handle, indent=4, default=str)
+                json.dump(self.detected, handle, indent=4, cls=CustomJSONEncoder)
 
     def serialize(self, record: dict) -> Union[dict, list, None]:
         raise NotImplementedError
diff --git a/tests/common/test_encoding.py b/tests/common/test_encoding.py
new file mode 100644
index 0000000..74c9274
--- /dev/null
+++ b/tests/common/test_encoding.py
@@ -0,0 +1,30 @@
+import json
+from datetime import datetime
+
+from mvt.common.encoding import CustomJSONEncoder
+
+
+class TestCustomJSONEncoder:
+    def test__normal_input(self):
+        assert json.dumps({"a": "b"}, cls=CustomJSONEncoder) == '{"a": "b"}'
+
+    def test__datetime_object(self):
+        assert (
+            json.dumps(
+                {"timestamp": datetime(2023, 11, 13, 12, 21, 49, 727467)},
+                cls=CustomJSONEncoder,
+            )
+            == '{"timestamp": "2023-11-13 12:21:49.727467"}'
+        )
+
+    def test__bytes_non_utf_8(self):
+        assert (
+            json.dumps({"identifier": b"\xa8\xa9"}, cls=CustomJSONEncoder)
+            == '{"identifier": "0xa8a9"}'
+        )
+
+    def test__bytes_valid_utf_8(self):
+        assert (
+            json.dumps({"name": "家".encode()}, cls=CustomJSONEncoder)
+            == '{"name": "\\u5bb6"}'
+        )