diff -r 1166b3321012 Lib/inspect.py
--- a/Lib/inspect.py	Thu Feb 13 12:48:54 2014 +0100
+++ b/Lib/inspect.py	Thu Feb 13 17:44:37 2014 -0500
@@ -1895,14 +1895,14 @@
 
             return sig.replace(parameters=new_params)
 
-    if _signature_is_builtin(obj):
-        return Signature.from_builtin(obj)
-
     if isfunction(obj) or _signature_is_functionlike(obj):
         # If it's a pure Python function, or an object that is duck type
         # of a Python function (Cython functions, for instance), then:
         return Signature.from_function(obj)
 
+    if _signature_is_builtin(obj):
+        return Signature.from_builtin(obj)
+
     if isinstance(obj, functools.partial):
         wrapped_sig = signature(obj.func)
         return _signature_get_partial(wrapped_sig, obj)
diff -r 1166b3321012 Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Thu Feb 13 12:48:54 2014 +0100
+++ b/Lib/test/test_inspect.py	Thu Feb 13 17:44:37 2014 -0500
@@ -14,6 +14,7 @@
 import types
 import unicodedata
 import unittest
+import unittest.mock
 
 try:
     from concurrent.futures import ThreadPoolExecutor
@@ -1789,6 +1790,21 @@
                            ('kwargs', ..., ..., "var_keyword")),
                            ...))
 
+        # Test with cython-like builtins:
+        _orig_isdesc = inspect.ismethoddescriptor
+        def _isdesc(obj):
+            if hasattr(obj, '_builtinmock'):
+                return True
+            return _orig_isdesc(obj)
+
+        with unittest.mock.patch('inspect.ismethoddescriptor', _isdesc):
+            builtin_func = funclike(func)
+            # Make sure that our mock setup is working
+            self.assertFalse(inspect.ismethoddescriptor(builtin_func))
+            builtin_func._builtinmock = True
+            self.assertTrue(inspect.ismethoddescriptor(builtin_func))
+            self.assertEqual(inspect.signature(builtin_func), sig_func)
+
     def test_signature_functionlike_class(self):
         # We only want to duck type function-like objects,
         # not classes.