diff --git a/MANIFEST.in b/MANIFEST.in
index 3e73ece4..e7cee955 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,5 +1,5 @@
 include README.rst
 include LICENSE.txt
 include AUTHORS.txt
-include jedi/mixin/*.py
+include jedi/mixin/*.pym
 recursive-exclude * *.pyc
diff --git a/jedi/builtin.py b/jedi/builtin.py
index 45a7ac5c..da4fc563 100644
--- a/jedi/builtin.py
+++ b/jedi/builtin.py
@@ -200,7 +200,7 @@ class Parser(CachedModule):
             if name == '__builtin__' and not is_py3k:
                 name = 'builtins'
             path = os.path.dirname(os.path.abspath(__file__))
-            with open(os.path.sep.join([path, 'mixin', name]) + '.py') as f:
+            with open(os.path.sep.join([path, 'mixin', name]) + '.pym') as f:
                 s = f.read()
         except IOError:
             return {}
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/datetime.py b/jedi/mixin/datetime.pym
similarity index 100%
rename from jedi/mixin/datetime.py
rename to jedi/mixin/datetime.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
diff --git a/setup.py b/setup.py
index 67cfdaed..9d6100c0 100644
--- a/setup.py
+++ b/setup.py
@@ -20,7 +20,7 @@ setup(name='jedi',
       keywords='python completion refactoring vim',
       long_description=readme,
       packages=['jedi'],
-      data_files={'jedi': ['mixin/*.py']},
+      package_data={'jedi': ['mixin/*.pym']},
       platforms=['any'],
       classifiers=[
           'Development Status :: 4 - Beta',