diff -r 27128cb4fea0 Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Mon Apr 13 21:49:11 2015 +0200
+++ b/Lib/test/test_inspect.py	Mon Apr 13 16:01:58 2015 -0400
@@ -1888,6 +1888,11 @@
         with self.assertRaisesRegex(ValueError, 'no signature found for builtin'):
             inspect.signature(_testcapi.docstring_no_signature)
 
+    @cpython_only
+    def test_signature_on_builtin_types_no_signature(self):
+        with self.assertRaisesRegex(TypeError, 'signature not supported for builtin type'):
+            inspect.signature(str)
+
     def test_signature_on_non_function(self):
         with self.assertRaisesRegex(TypeError, 'is not a callable object'):
             inspect.signature(42)