diff --git a/jedi/builtin.py b/jedi/builtin.py
index 1802ffd4..3b8ea3d4 100644
--- a/jedi/builtin.py
+++ b/jedi/builtin.py
@@ -193,7 +193,7 @@ class Parser(CachedModule):
             if name == '__builtin__' and not is_py3k:
                 name = 'builtins'
             path = os.path.dirname(os.path.abspath(__file__))
-            f = open(os.path.sep.join([path, 'mixin', name]) + '.py')
+            f = open(os.path.sep.join([path, 'mixin', name]) + '.pym')
         except IOError:
             return {}
         else:
diff --git a/jedi/mixin/_functools.py b/jedi/mixin/_functools.pym
similarity index 100%
rename from jedi/mixin/_functools.py
rename to jedi/mixin/_functools.pym
diff --git a/jedi/mixin/_sre.py b/jedi/mixin/_sre.pym
similarity index 100%
rename from jedi/mixin/_sre.py
rename to jedi/mixin/_sre.pym
diff --git a/jedi/mixin/_weakref.py b/jedi/mixin/_weakref.pym
similarity index 100%
rename from jedi/mixin/_weakref.py
rename to jedi/mixin/_weakref.pym
diff --git a/jedi/mixin/builtins.py b/jedi/mixin/builtins.pym
similarity index 100%
rename from jedi/mixin/builtins.py
rename to jedi/mixin/builtins.pym
diff --git a/jedi/mixin/posix.py b/jedi/mixin/posix.pym
similarity index 100%
rename from jedi/mixin/posix.py
rename to jedi/mixin/posix.pym