diff --git a/bec_server/bec_server/scan_server/tests/scan_fixtures.py b/bec_server/bec_server/scan_server/tests/scan_fixtures.py
index e7f3b23e9..150510f82 100644
--- a/bec_server/bec_server/scan_server/tests/scan_fixtures.py
+++ b/bec_server/bec_server/scan_server/tests/scan_fixtures.py
@@ -386,6 +386,8 @@ def _assemble_scan(scan_type, *scan_args, **scan_kwargs):
             if name in devices:
                 continue
             devices[name] = _MockDevice(name)
+        for name, device in custom_devices.items():
+            devices[name] = device
         scan_device_manager = SimpleNamespace(devices=devices, connector=connector)
         resolved_scan_kwargs = {"system_config": {}, **scan_kwargs}