diff --git a/conftest.py b/conftest.py
index 5c27d947c13..d71de30a616 100644
--- a/conftest.py
+++ b/conftest.py
@@ -15,6 +15,9 @@
 import pytest  # noqa: E402
 
 from keras.src.backend import backend  # noqa: E402
+from keras.src.saving.object_registration import (  # noqa: E402
+    get_custom_objects,
+)
 
 
 def pytest_configure(config):
@@ -32,3 +35,9 @@ def pytest_collection_modifyitems(config, items):
     for item in items:
         if "requires_trainable_backend" in item.keywords:
             item.add_marker(requires_trainable_backend)
+
+
+# Ensure each test is run in isolation regarding the custom objects dict
+@pytest.fixture(autouse=True)
+def reset_custom_objects_global_dictionary(request):
+    get_custom_objects().clear()
diff --git a/keras/src/models/model_test.py b/keras/src/models/model_test.py
index 7fa91c5b95d..cd06e154616 100644
--- a/keras/src/models/model_test.py
+++ b/keras/src/models/model_test.py
@@ -1,5 +1,7 @@
 import pickle
+import sys
 
+import cloudpickle
 import numpy as np
 import pytest
 from absl.testing import parameterized
@@ -11,6 +13,7 @@
 from keras.src.models.functional import Functional
 from keras.src.models.model import Model
 from keras.src.models.model import model_from_json
+from keras.src.saving.object_registration import register_keras_serializable
 
 
 def _get_model():
@@ -68,6 +71,17 @@ def _get_model_multi_outputs_dict():
     return model
 
 
+@pytest.fixture
+def fake_main_module(request, monkeypatch):
+    original_main = sys.modules["__main__"]
+
+    def restore_main_module():
+        sys.modules["__main__"] = original_main
+
+    request.addfinalizer(restore_main_module)
+    sys.modules["__main__"] = sys.modules[__name__]
+
+
 @pytest.mark.requires_trainable_backend
 class ModelTest(testing.TestCase, parameterized.TestCase):
     def test_functional_rerouting(self):
@@ -141,6 +155,45 @@ def test_functional_pickling(self, model_fn):
 
         self.assertAllClose(np.array(pred_reloaded), np.array(pred))
 
+    # Fake the __main__ module because cloudpickle only serializes
+    # functions & classes if they are defined in the __main__ module.
+    @pytest.mark.usefixtures("fake_main_module")
+    def test_functional_pickling_custom_layer(self):
+        @register_keras_serializable()
+        class CustomDense(layers.Layer):
+            def __init__(self, units, **kwargs):
+                super().__init__(**kwargs)
+                self.units = units
+                self.dense = layers.Dense(units)
+
+            def call(self, x):
+                return self.dense(x)
+
+            def get_config(self):
+                config = super().get_config()
+                config.update({"units": self.units})
+                return config
+
+        x = Input(shape=(3,), name="input_a")
+        output_a = CustomDense(10, name="output_a")(x)
+        model = Model(x, output_a)
+
+        self.assertIsInstance(model, Functional)
+        model.compile()
+        x = np.random.rand(8, 3)
+
+        dumped_pickle = cloudpickle.dumps(model)
+
+        # Verify that we can load the dumped pickle even if the custom object
+        # is not available in the loading environment.
+        del CustomDense
+        reloaded_pickle = cloudpickle.loads(dumped_pickle)
+
+        pred_reloaded = reloaded_pickle.predict(x)
+        pred = model.predict(x)
+
+        self.assertAllClose(np.array(pred_reloaded), np.array(pred))
+
     @parameterized.named_parameters(
         ("single_output_1", _get_model_single_output, None),
         ("single_output_2", _get_model_single_output, "list"),
diff --git a/keras/src/saving/keras_saveable.py b/keras/src/saving/keras_saveable.py
index 7fc536b470c..e122a4fa8d3 100644
--- a/keras/src/saving/keras_saveable.py
+++ b/keras/src/saving/keras_saveable.py
@@ -1,5 +1,7 @@
 import io
 
+from keras.src.saving.object_registration import get_custom_objects
+
 
 class KerasSaveable:
     # Note: renaming this function will cause old pickles to be broken.
@@ -14,12 +16,23 @@ def _obj_type(self):
         )
 
     @classmethod
-    def _unpickle_model(cls, bytesio):
+    def _unpickle_model(cls, data):
         import keras.src.saving.saving_lib as saving_lib
 
         # pickle is not safe regardless of what you do.
+
+        if "custom_objects_buf" in data.keys():
+            import pickle
+
+            custom_objects = pickle.load(data["custom_objects_buf"])
+        else:
+            custom_objects = None
+
         return saving_lib._load_model_from_fileobj(
-            bytesio, custom_objects=None, compile=True, safe_mode=False
+            data["model_buf"],
+            custom_objects=custom_objects,
+            compile=True,
+            safe_mode=False,
         )
 
     def __reduce__(self):
@@ -30,9 +43,23 @@ def __reduce__(self):
         keras saving library."""
         import keras.src.saving.saving_lib as saving_lib
 
-        buf = io.BytesIO()
-        saving_lib._save_model_to_fileobj(self, buf, "h5")
+        data = {}
+
+        model_buf = io.BytesIO()
+        saving_lib._save_model_to_fileobj(self, model_buf, "h5")
+        data["model_buf"] = model_buf
+
+        try:
+            import cloudpickle
+
+            custom_objects_buf = io.BytesIO()
+            cloudpickle.dump(get_custom_objects(), custom_objects_buf)
+            custom_objects_buf.seek(0)
+            data["custom_objects_buf"] = custom_objects_buf
+        except ImportError:
+            pass
+
         return (
             self._unpickle_model,
-            (buf,),
+            (data,),
         )