diff --git a/OpenSSL/crypto.py b/OpenSSL/crypto.py
index 15e3b6a..bb4c0ea 100644
--- a/OpenSSL/crypto.py
+++ b/OpenSSL/crypto.py
@@ -218,6 +218,8 @@
         if name.startswith('_'):
             return super(X509Name, self).__setattr__(name, value)
 
+        # Note: we really do not want str subclasses here, so we do not use
+        # isinstance.
         if type(name) is not str:
             raise TypeError("attribute name must be string, not '%.200s'" % (
                     type(value).__name__,))
diff --git a/OpenSSL/test/test_crypto.py b/OpenSSL/test/test_crypto.py
index d461d8b..54c9a37 100644
--- a/OpenSSL/test/test_crypto.py
+++ b/OpenSSL/test/test_crypto.py
@@ -697,12 +697,14 @@
         # rejected.  Sorry, you're wrong.  unicode is automatically converted to
         # str outside of the control of X509Name, so there's no way to reject
         # it.
+
+        # Also, this used to test str subclasses, but that test is less relevant
+        # now that the implementation is in Python instead of C.  Also PyPy
+        # automatically converts str subclasses to str when they are passed to
+        # setattr, so we can't test it on PyPy.  Apparently CPython does this
+        # sometimes as well.
         self.assertRaises(TypeError, setattr, name, None, "hello")
         self.assertRaises(TypeError, setattr, name, 30, "hello")
-        class evil(str):
-            pass
-        self.assertRaises(TypeError, setattr, name, evil(), "hello")
-
 
     def test_setInvalidAttribute(self):
         """