diff --git a/asdf/_tests/test_asdf.py b/asdf/_tests/test_asdf.py
index 1501f3a21..e408b2d70 100644
--- a/asdf/_tests/test_asdf.py
+++ b/asdf/_tests/test_asdf.py
@@ -125,10 +125,7 @@ def test_asdf_file_extensions():
         af.extensions = arg
         assert af.extensions == [ExtensionProxy(extension)]
 
-    msg = (
-        r"[The extensions parameter must be an extension.*, "
-        r"Extension must implement the Extension or AsdfExtension interface]"
-    )
+    msg = r"[The extensions parameter must be an extension.*, Extension must implement the Extension interface]"
     for arg in (object(), [object()]):
         with pytest.raises(TypeError, match=msg):
             AsdfFile(extensions=arg)
@@ -185,10 +182,7 @@ def test_open_asdf_extensions(tmp_path):
         with open_asdf(path, extensions=arg) as af:
             assert af.extensions == [ExtensionProxy(extension)]
 
-    msg = (
-        r"[The extensions parameter must be an extension.*, "
-        r"Extension must implement the Extension or AsdfExtension interface]"
-    )
+    msg = r"[The extensions parameter must be an extension.*, Extension must implement the Extension interface]"
     for arg in (object(), [object()]):
         with pytest.raises(TypeError, match=msg), open_asdf(path, extensions=arg) as af:
             pass
@@ -211,7 +205,7 @@ def test_serialization_context():
 
     assert context.url == context._url == "file://test.asdf"
 
-    with pytest.raises(TypeError, match=r"Extension must implement the Extension or AsdfExtension interface"):
+    with pytest.raises(TypeError, match=r"Extension must implement the Extension interface"):
         context._mark_extension_used(object())
 
     with pytest.raises(ValueError, match=r"ASDF Standard version .* is not supported by asdf==.*"):
diff --git a/asdf/_tests/test_entry_points.py b/asdf/_tests/test_entry_points.py
index baaed37ba..ec45ca05d 100644
--- a/asdf/_tests/test_entry_points.py
+++ b/asdf/_tests/test_entry_points.py
@@ -151,7 +151,7 @@ def test_get_extensions(mock_entry_points):
     )
     with pytest.warns(
         AsdfWarning,
-        match=r"TypeError: Extension must implement the Extension or AsdfExtension interface",
+        match=r"TypeError: Extension must implement the Extension interface",
     ):
         extensions = entry_points.get_extensions()
     assert len(extensions) == 2
diff --git a/asdf/_tests/test_extension.py b/asdf/_tests/test_extension.py
index affdd3dce..bb2a40b19 100644
--- a/asdf/_tests/test_extension.py
+++ b/asdf/_tests/test_extension.py
@@ -162,7 +162,7 @@ def test_extension_proxy_maybe_wrap():
     assert proxy.delegate is extension
     assert ExtensionProxy.maybe_wrap(proxy) is proxy
 
-    with pytest.raises(TypeError, match=r"Extension must implement the Extension or AsdfExtension interface"):
+    with pytest.raises(TypeError, match=r"Extension must implement the Extension interface"):
         ExtensionProxy.maybe_wrap(object())
 
 
@@ -241,7 +241,7 @@ def test_extension_proxy():
     assert proxy.class_name == "asdf._tests.test_extension.FullExtension"
 
     # Should fail when the input is not one of the two extension interfaces:
-    with pytest.raises(TypeError, match=r"Extension must implement the Extension or AsdfExtension interface"):
+    with pytest.raises(TypeError, match=r"Extension must implement the Extension interface"):
         ExtensionProxy(object)
 
     # Should fail with a bad converter:
diff --git a/asdf/extension/_extension.py b/asdf/extension/_extension.py
index 11a288ed0..d19ce81ac 100644
--- a/asdf/extension/_extension.py
+++ b/asdf/extension/_extension.py
@@ -147,7 +147,7 @@ def maybe_wrap(cls, delegate):
 
     def __init__(self, delegate, package_name=None, package_version=None):
         if not isinstance(delegate, (Extension, _AsdfExtension)):
-            msg = "Extension must implement the Extension or AsdfExtension interface"
+            msg = "Extension must implement the Extension interface"
             raise TypeError(msg)
 
         self._delegate = delegate
diff --git a/asdf/extension/_manager.py b/asdf/extension/_manager.py
index 3509a201d..155f84914 100644
--- a/asdf/extension/_manager.py
+++ b/asdf/extension/_manager.py
@@ -203,7 +203,7 @@ def get_cached_extension_manager(extensions):
 
     Parameters
     ----------
-    extensions : list of asdf.extension.AsdfExtension or asdf.extension.Extension
+    extensions : list of asdf.extension.Extension
 
     Returns
     -------