diff -r 37905786b34b Lib/inspect.py
--- a/Lib/inspect.py	Sun Apr 12 23:24:17 2015 -0500
+++ b/Lib/inspect.py	Mon Apr 13 13:20:05 2015 -0400
@@ -2131,9 +2131,12 @@
             if type not in obj.__mro__:
                 # We have a class (not metaclass), but no user-defined
                 # __init__ or __new__ for it
-                if obj.__init__ is object.__init__:
+                if obj.__new__ is object.__new__ and obj.__init__ is object.__init__:
                     # Return a signature of 'object' builtin.
                     return signature(object)
+                else:
+                    msg = 'signature not supported for builtin type {!r}'.format(obj)
+                    raise TypeError(msg)
 
     elif not isinstance(obj, _NonUserDefinedCallables):
         # An object with __call__