diff --git a/_delb/plugins/core_loaders.py b/_delb/plugins/core_loaders.py
index 367f7894..9872c96f 100644
--- a/_delb/plugins/core_loaders.py
+++ b/_delb/plugins/core_loaders.py
@@ -26,6 +26,7 @@
 from io import IOBase, UnsupportedOperation
 from pathlib import Path
 from typing import TYPE_CHECKING, cast, Any
+from warnings import warn
 
 from lxml import etree
 
@@ -60,8 +61,16 @@ def etree_loader(data: Any, config: SimpleNamespace) -> LoaderResult:
     :class:`lxml.etree._ElementTree` instances.
     """
     if isinstance(data, etree._ElementTree):
+        warn(
+            "lxml's etree models will not be usable inputs with the contributed core loaders.",
+            category=DeprecationWarning,
+        )
         return deepcopy(data)
     if isinstance(data, etree._Element):
+        warn(
+            "lxml's etree models will not be usable inputs with the contributed core loaders.",
+            category=DeprecationWarning,
+        )
         return etree.ElementTree(
             element=deepcopy(data), parser=config.parser_options._make_parser()
         )
diff --git a/tests/test_loaders.py b/tests/test_loaders.py
index 43a8a5dc..45c65690 100644
--- a/tests/test_loaders.py
+++ b/tests/test_loaders.py
@@ -23,7 +23,8 @@ def test_etree_loader():
     tree = etree.parse(str(TEST_FILE))
     root = tree.getroot()
 
-    document = Document(root)
+    with pytest.deprecated_call():
+        document = Document(root)
     assert document.root._etree_obj is not root
     assert document.source_url is None