diff --git a/setup.cfg b/setup.cfg
index 495d397..63cfd69 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -37,6 +37,7 @@ install_requires =
     beangulp
     scikit-learn>=1.0
     numpy>=1.18.0
+    typing-extensions>=4.9
 
 [options.packages.find]
 exclude =
diff --git a/smart_importer/detector.py b/smart_importer/detector.py
index 71b7bfa..5a50202 100644
--- a/smart_importer/detector.py
+++ b/smart_importer/detector.py
@@ -7,12 +7,16 @@
 
 from beancount.core import data
 from beangulp import Importer, similar
+from typing_extensions import deprecated
 
 from smart_importer.hooks import ImporterHook
 
 logger = logging.getLogger(__name__)  # pylint: disable=invalid-name
 
 
+@deprecated(
+    "Use or override the deduplicate method on beangulp.Importer directly."
+)
 class DuplicateDetector(ImporterHook):
     """Class for duplicate detector importer helpers.