diff --git a/bson/json_util.py b/bson/json_util.py
index ada6e89c5..e6bc562d6 100644
--- a/bson/json_util.py
+++ b/bson/json_util.py
@@ -852,7 +852,7 @@ def _encode_int64(obj: Int64, json_options: JSONOptions) -> Any:
     if json_options.strict_number_long:
         return {"$numberLong": str(obj)}
     else:
-        return obj
+        return int(obj)
 
 
 # Encoders for BSON types
diff --git a/doc/changelog.rst b/doc/changelog.rst
index 98f535245..62bd6d851 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -14,6 +14,14 @@ PyMongo 4.7 brings a number of improvements including:
 - Replaced usage of :class:`bson.son.SON` on all internal classes and commands to dict,
   :attr:`options.pool_options.metadata` is now of type ``dict`` as opposed to :class:`bson.son.SON`.
 - Significantly improved the performance of encoding BSON documents to JSON.
+- Fixed a bug where :class:`~bson.int64.Int64` instances could not always be encoded by `orjson`_. The following now
+  works::
+
+    >>> import orjson
+    >>> from bson import json_util
+    >>> orjson.dumps({'a': Int64(1)}, default=json_util.default, option=orjson.OPT_PASSTHROUGH_SUBCLASS)
+
+.. _orjson: https://github.com/ijl/orjson
 
 Changes in Version 4.6.1
 ------------------------
diff --git a/test/test_json_util.py b/test/test_json_util.py
index 003593f59..43007808c 100644
--- a/test/test_json_util.py
+++ b/test/test_json_util.py
@@ -545,6 +545,13 @@ class TestJsonUtil(unittest.TestCase):
         self.assertEqual(json_util.dumps({"weight": Int64(65535)}), '{"weight": 65535}')
         json_options = JSONOptions(strict_number_long=True, json_mode=JSONMode.LEGACY)
         self.assertEqual(json_util.dumps({"weight": Int64(65535)}, json_options=json_options), jsn)
+        # Ensure json_util.default converts Int64 to int in non-strict mode.
+        converted = json_util.default(Int64(65535))
+        self.assertEqual(converted, 65535)
+        self.assertNotIsInstance(converted, Int64)
+        self.assertEqual(
+            json_util.default(Int64(65535), json_options=json_options), {"$numberLong": "65535"}
+        )
 
     def test_loads_document_class(self):
         # document_class dict should always work