diff --git a/asdf/tests/test_deprecated.py b/asdf/tests/test_deprecated.py
index 49746b5f0..767148bad 100644
--- a/asdf/tests/test_deprecated.py
+++ b/asdf/tests/test_deprecated.py
@@ -84,3 +84,14 @@ def test_default_resolver():
 def test_get_cached_asdf_extension_list_deprecation():
     with pytest.warns(AsdfDeprecationWarning, match="get_cached_asdf_extension_list is deprecated"):
         asdf.extension.get_cached_asdf_extension_list([])
+
+
+@pytest.mark.parametrize("name", ["AsdfExtension", "AsdfExtensionList", "BuiltinExtension"])
+def test_extension_class_deprecation(name):
+    with pytest.warns(AsdfDeprecationWarning, match=f"{name} is deprecated"):
+        getattr(asdf.extension, name)
+
+
+def test_top_level_asdf_extension_deprecation():
+    with pytest.warns(AsdfDeprecationWarning, match="AsdfExtension is deprecated"):
+        asdf.AsdfExtension