diff --git a/homeassistant/helpers/device_registry.py b/homeassistant/helpers/device_registry.py
index cb336d1455b..962cd01bf00 100644
--- a/homeassistant/helpers/device_registry.py
+++ b/homeassistant/helpers/device_registry.py
@@ -820,7 +820,9 @@ class DeviceRegistry(BaseRegistry[dict[str, list[dict[str, Any]]]]):
             )
 
         if merge_identifiers is not UNDEFINED and new_identifiers is not UNDEFINED:
-            raise HomeAssistantError
+            raise HomeAssistantError(
+                "Cannot define both merge_identifiers and new_identifiers"
+            )
 
         if isinstance(disabled_by, str) and not isinstance(
             disabled_by, DeviceEntryDisabler