diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3b08ecbfe..a493bc934 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # PyNWB Changelog
 
+## PyNWB 4.1.1 (Unreleased)
+
+### Fixed
+- Fixed `mock_DeviceModel` defaulting `manufacturer` to `None`, which made every call raise `TypeError: DeviceModel.__init__: None is not allowed for 'manufacturer'` because `DeviceModel` requires `manufacturer` to be a `str`. The mock now defaults it to `"manufacturer"`, matching the other mock defaults, and is covered by the parametrized `test_mock`/`test_mock_write` tests. @HugoFara [#2232](https://github.com/NeurodataWithoutBorders/pynwb/pull/2232)
+
+
 ## PyNWB 4.1.0 (July 23, 2026)
 
 ### Changed
diff --git a/src/pynwb/testing/mock/device.py b/src/pynwb/testing/mock/device.py
index 4499cc01d..9124e8e1a 100644
--- a/src/pynwb/testing/mock/device.py
+++ b/src/pynwb/testing/mock/device.py
@@ -26,7 +26,7 @@ def mock_Device(
 
 def mock_DeviceModel(
     name: Optional[str] = None,
-    manufacturer: str = None,
+    manufacturer: str = "manufacturer",
     model_number: Optional[str] = None,
     description: str = "description",
     nwbfile: Optional[NWBFile] = None,
diff --git a/tests/unit/test_mock.py b/tests/unit/test_mock.py
index f0b805337..2fc202634 100644
--- a/tests/unit/test_mock.py
+++ b/tests/unit/test_mock.py
@@ -23,7 +23,7 @@
     mock_OptogeneticSeries
 )
 
-from pynwb.testing.mock.device import mock_Device
+from pynwb.testing.mock.device import mock_Device, mock_DeviceModel
 
 from pynwb.testing.mock.behavior import (
     mock_Position,
@@ -68,6 +68,7 @@
     mock_OptogeneticStimulusSite,
     mock_OptogeneticSeries,
     mock_Device,
+    mock_DeviceModel,
     mock_Position,
     mock_PupilTracking,
     mock_CompassDirection,