diff --git a/spacy/errors.py b/spacy/errors.py
index b97ef3a8e..d99c96922 100644
--- a/spacy/errors.py
+++ b/spacy/errors.py
@@ -5,13 +5,13 @@ from __future__ import unicode_literals
 def add_codes(err_cls):
     """Add error codes to string messages via class attribute names."""
 
-    class ErrorsWithCodes(object):
+    class ErrorsWithCodes(err_cls):
         def __getattribute__(self, code):
-            if not code.startswith('__'):
-                msg = getattr(err_cls, code)
-                return "[{code}] {msg}".format(code=code, msg=msg)
+            msg = super().__getattribute__(code)
+            if code.startswith('__'):  # python system attributes like __class__
+                return msg
             else:
-                return super().__getattribute__(code)
+                return "[{code}] {msg}".format(code=code, msg=msg)
 
     return ErrorsWithCodes()
 
diff --git a/spacy/tests/test_errors.py b/spacy/tests/test_errors.py
index ba24f4456..1bd4eec7f 100644
--- a/spacy/tests/test_errors.py
+++ b/spacy/tests/test_errors.py
@@ -1,5 +1,7 @@
 from inspect import isclass
 
+import pytest
+
 from spacy.errors import add_codes
 
 
@@ -10,4 +12,6 @@ class Errors(object):
 
 def test_add_codes():
     assert Errors.E001 == "[E001] error description"
+    with pytest.raises(AttributeError):
+        Errors.E002
     assert isclass(Errors.__class__)