diff --git a/netbox/dcim/api/serializers_/devices.py b/netbox/dcim/api/serializers_/devices.py
index 110fce97e..ee543df24 100644
--- a/netbox/dcim/api/serializers_/devices.py
+++ b/netbox/dcim/api/serializers_/devices.py
@@ -203,6 +203,7 @@ class ModuleSerializer(PrimaryModelSerializer):
         module_type = data.get('module_type')
         module_bay = data.get('module_bay')
 
+        # Required-field validation fires separately; skip here if any are missing.
         if not all([device, module_type, module_bay]):
             return data
 
@@ -238,8 +239,7 @@ class ModuleSerializer(PrimaryModelSerializer):
                     if template.name.count(MODULE_TOKEN) != len(module_bays):
                         raise serializers.ValidationError(
                             _(
-                                "Cannot install module with placeholder values in a module bay tree {level} in tree "
-                                "but {tokens} placeholders given."
+                                "Cannot install module with {tokens} placeholder(s) in a module bay at depth {level}."
                             ).format(
                                 level=len(module_bays), tokens=template.name.count(MODULE_TOKEN)
                             )
@@ -274,8 +274,8 @@ class ModuleSerializer(PrimaryModelSerializer):
         # Tags are handled after save; pop them here to pass to _save_tags()
         tags = validated_data.pop('tags', None)
 
-        # Build the instance without saving so we can set private attributes
-        # that control component replication behaviour in Module.save()
+        # _adopt_components and _disable_replication must be set on the instance before
+        # save() is called, so we cannot delegate to super().create() here.
         instance = self.Meta.model(**validated_data)
         if adopt_components:
             instance._adopt_components = True
diff --git a/netbox/dcim/tests/test_api.py b/netbox/dcim/tests/test_api.py
index 3128b6fc0..65b14bd6c 100644
--- a/netbox/dcim/tests/test_api.py
+++ b/netbox/dcim/tests/test_api.py
@@ -1846,9 +1846,42 @@ class ModuleTest(APIViewTestCases.APIViewTestCase):
         }
         response = self.client.patch(url, data, format='json', **self.header)
         self.assertHttpStatus(response, status.HTTP_200_OK)
+        self.assertEqual(response.data['serial'], 'PATCHED')
         # No interfaces should have been created by the PATCH
         self.assertFalse(device.interfaces.exists())
 
+    def test_adopt_and_replicate_components(self):
+        """
+        Installing a module with both adopt_components=True and replicate_components=True
+        should adopt existing unowned components and create new components for templates
+        that have no matching existing component.
+        """
+        self.add_permissions('dcim.add_module')
+        manufacturer = Manufacturer.objects.get(name='Generic')
+        device = create_test_device('Device for Adopt+Replicate Test')
+        module_type = ModuleType.objects.create(manufacturer=manufacturer, model='Adopt+Replicate Test Module Type')
+        InterfaceTemplate.objects.create(module_type=module_type, name='eth0', type='1000base-t')
+        InterfaceTemplate.objects.create(module_type=module_type, name='eth1', type='1000base-t')
+        module_bay = ModuleBay.objects.create(device=device, name='Adopt+Replicate Bay')
+        # eth0 already exists (unowned); eth1 does not
+        existing_iface = Interface.objects.create(device=device, name='eth0', type='1000base-t')
+
+        url = reverse('dcim-api:module-list')
+        data = {
+            'device': device.pk,
+            'module_bay': module_bay.pk,
+            'module_type': module_type.pk,
+            'adopt_components': True,
+            'replicate_components': True,
+        }
+        response = self.client.post(url, data, format='json', **self.header)
+        self.assertHttpStatus(response, status.HTTP_201_CREATED)
+        # eth0 should have been adopted (now owned by the new module)
+        existing_iface.refresh_from_db()
+        self.assertIsNotNone(existing_iface.module)
+        # eth1 should have been created
+        self.assertTrue(device.interfaces.filter(name='eth1').exists())
+
 
 class ConsolePortTest(Mixins.ComponentTraceMixin, APIViewTestCases.APIViewTestCase):
     model = ConsolePort