diff --git a/py/__init__.py b/py/__init__.py
index ad9d6c2a4..a7c63f58a 100644
--- a/py/__init__.py
+++ b/py/__init__.py
@@ -133,7 +133,7 @@ initpkg(__name__,
     'code.getrawcode'        : ('./code/code.py', 'getrawcode'),
     'code.patch_builtins'    : ('./code/code.py', 'patch_builtins'),
     'code.unpatch_builtins'  : ('./code/code.py', 'unpatch_builtins'),
-    'code._AssertionError'   : ('./code/assertion.py', 'AssertionError'),
+    'code._AssertionError'   : ('./code/_assertion.py', 'AssertionError'),
 
     # backports and additions of builtins
     'builtin.__doc__'        : ('./builtin/__init__.py', '__doc__'),
diff --git a/py/code/code.py b/py/code/code.py
index 2581a978c..7083d7ad9 100644
--- a/py/code/code.py
+++ b/py/code/code.py
@@ -739,10 +739,10 @@ oldbuiltins = {}
 def patch_builtins(assertion=True, compile=True):
     """ put compile and AssertionError builtins to Python's builtins. """
     if assertion:
-        from py.__.code import assertion
+        from py.__.code import _assertion
         l = oldbuiltins.setdefault('AssertionError', [])
         l.append(py.builtin.builtins.AssertionError)
-        py.builtin.builtins.AssertionError = assertion.AssertionError
+        py.builtin.builtins.AssertionError = _assertion.AssertionError
     if compile: 
         l = oldbuiltins.setdefault('compile', [])
         l.append(py.builtin.builtins.compile)