diff --git a/Objects/classobject.c b/Objects/classobject.c
index e739cc6..7680a3d 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -2256,6 +2256,8 @@
 	PyObject *self;
 	PyObject *classObj = NULL;
 
+	if (!_PyArg_NoKeywords("instancemethod", kw))
+		return NULL;
 	if (!PyArg_UnpackTuple(args, "instancemethod", 2, 3,
 			      &func, &self, &classObj))
 		return NULL;