diff --git a/funcsigs/__init__.py b/funcsigs/__init__.py
index 5f5378b..c9ede7c 100644
--- a/funcsigs/__init__.py
+++ b/funcsigs/__init__.py
@@ -20,8 +20,8 @@
 __all__ = ['BoundArguments', 'Parameter', 'Signature', 'signature']
 
 
-_WrapperDescriptor = type(type.__call__)
-_MethodWrapper = type(all.__call__)
+_WrapperDescriptor = type(bytearray.__add__)
+_MethodWrapper = type(u'str'.__add__)
 
 _NonUserDefinedCallables = (_WrapperDescriptor,
                             _MethodWrapper,