diff --git a/CHANGELOG.md b/CHANGELOG.md
index 158316e59a..8023ce7edb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,13 @@
 
 All notable changes to this project will be documented in this file. See [standard-version](https://github.com/conventional-changelog/standard-version) for commit guidelines.
 
+## [1.103.1](https://github.com/aws/jsii/compare/v1.103.0...v1.103.1) (2024-08-30)
+
+
+### Bug Fixes
+
+* **python:** user defined `__jsii_proxy_class` attributes are not preserved  ([#4625](https://github.com/aws/jsii/issues/4625)) ([d3ec911](https://github.com/aws/jsii/commit/d3ec911a5d531e088524d2479e1ee831da0bc2ff))
+
 ## [1.103.0](https://github.com/aws/jsii/compare/v1.102.0...v1.103.0) (2024-08-27)
 
 
diff --git a/lerna.json b/lerna.json
index e77f0c1658..d4a22cc5bc 100644
--- a/lerna.json
+++ b/lerna.json
@@ -12,6 +12,6 @@
       "rejectCycles": true
     }
   },
-  "version": "1.103.0",
+  "version": "1.103.1",
   "$schema": "node_modules/lerna/schemas/lerna-schema.json"
 }
diff --git a/packages/@jsii/python-runtime/src/jsii/_runtime.py b/packages/@jsii/python-runtime/src/jsii/_runtime.py
index 35c3385300..7d7cb1b469 100644
--- a/packages/@jsii/python-runtime/src/jsii/_runtime.py
+++ b/packages/@jsii/python-runtime/src/jsii/_runtime.py
@@ -168,7 +168,7 @@ def implements(*interfaces: Type[Any]) -> Callable[[T], T]:
     def deco(cls):
         cls.__jsii_type__ = getattr(cls, "__jsii_type__", None)
         cls.__jsii_ifaces__ = getattr(cls, "__jsii_ifaces__", []) + list(interfaces)
-        cls.__jsii_proxy_class__ = lambda: getattr(cls, "__jsii_proxy_class__", None)
+        cls.__jsii_proxy_class__ = getattr(cls, "__jsii_proxy_class__", lambda: None)
 
         # https://github.com/agronholm/typeguard/issues/479
         cls.__protocol_attrs__ = getattr(cls, "__protocol_attrs__", [])
diff --git a/packages/@jsii/python-runtime/tests/test_python.py b/packages/@jsii/python-runtime/tests/test_python.py
index 1aaa087ae6..991185f2d0 100644
--- a/packages/@jsii/python-runtime/tests/test_python.py
+++ b/packages/@jsii/python-runtime/tests/test_python.py
@@ -27,6 +27,37 @@ def test_inheritance_maintained(self):
 
         assert base_names == ["DerivedStruct", "MyFirstStruct"]
 
+
+class TestImplementsInterface:
+
+    def test_jsii_proxy_class_defaults_to_none(self) -> None:
+        @jsii.implements(IBaz)
+        class MyBaz:
+            pass
+
+        klass = getattr(MyBaz, "__jsii_proxy_class__")()
+        assert klass == None
+
+    def test_jsii_proxy_class_preserves_user_defined_attribute(self) -> None:
+
+        class _MyBazProxy:
+            def baz_method(self) -> str:
+                return "_MyBazProxy"
+
+        @jsii.implements(IBaz)
+        class MyBaz:
+
+            @staticmethod
+            def __jsii_proxy_class__():
+                return _MyBazProxy
+
+            def baz_method(self) -> str:
+                return "MyBaz"
+
+        klass = getattr(MyBaz, "__jsii_proxy_class__")()
+        instance = klass()
+        assert instance.baz_method() == "_MyBazProxy"
+
     def test_implements_interface(self) -> None:
         """Checks that jsii-generated classes correctly implement the relevant jsii-generated interfaces."""