diff --git a/src/pluggy/_manager.py b/src/pluggy/_manager.py
index 8a0959f7..1d7984a9 100644
--- a/src/pluggy/_manager.py
+++ b/src/pluggy/_manager.py
@@ -440,7 +440,7 @@ def _verify_hook(self, hook: HookCaller, hookimpl: HookImpl) -> None:
             )
 
         if hook.spec.warn_on_impl_args:
-            for hookimpl_argname in hookimpl.argnames:
+            for hookimpl_argname in hookimpl.argnames + hookimpl.kwargnames:
                 argname_warning = hook.spec.warn_on_impl_args.get(hookimpl_argname)
                 if argname_warning is not None:
                     _warn_for_function(argname_warning, hookimpl.function)
diff --git a/testing/test_details.py b/testing/test_details.py
index 8df167f4..3a9858f8 100644
--- a/testing/test_details.py
+++ b/testing/test_details.py
@@ -128,6 +128,30 @@ def foo(self, old2, old1, new):
     assert record2.lineno == Plugin.foo.__code__.co_firstlineno
 
 
+def test_warn_when_deprecated_args_with_defaults_specified() -> None:
+    warning = DeprecationWarning("old is deprecated")
+
+    class Spec:
+        @hookspec(warn_on_impl_args={"old": warning})
+        def foo(self, old=None, new=None):
+            raise NotImplementedError()
+
+    class Plugin:
+        @hookimpl
+        def foo(self, old=None, new=None):
+            raise NotImplementedError()
+
+    pm = PluginManager(hookspec.project_name)
+    pm.add_hookspecs(Spec)
+
+    with pytest.warns(DeprecationWarning) as records:
+        pm.register(Plugin())
+    (record,) = records
+    assert record.message is warning
+    assert record.filename == Plugin.foo.__code__.co_filename
+    assert record.lineno == Plugin.foo.__code__.co_firstlineno
+
+
 def test_plugin_getattr_raises_errors() -> None:
     """Pluggy must be able to handle plugins which raise weird exceptions
     when getattr() gets called (#11).