diff --git a/cython_multibuild/__init__.py b/cython_multibuild/__init__.py
index 0b4c785ca475c9b7d96ce3ffdc4cfe0f05d2402f..1b207f7abf91070c6a398776179c1b302cafcb7a 100644
--- a/cython_multibuild/__init__.py
+++ b/cython_multibuild/__init__.py
@@ -1,4 +1,4 @@
 from .build import build
 from .multibuild import Multibuild
 
-__version__ = '0.2'
\ No newline at end of file
+__version__ = '0.3'
diff --git a/cython_multibuild/multibuild.py b/cython_multibuild/multibuild.py
index fd9557c803ea4188eac070ac8239754bf71eab11..e41ba7d9b77e42173b518e94bf3b2c4078bd39d1 100644
--- a/cython_multibuild/multibuild.py
+++ b/cython_multibuild/multibuild.py
@@ -6,6 +6,7 @@ from setuptools import Extension
 
 logger = logging.getLogger(__name__)
 
+SEP_LEN = len(os.path.sep)
 
 class Multibuild:
     def __init__(self, extension_name: str, files: tp.Iterable[str]):
@@ -152,10 +153,10 @@ def bootstrap_cython_submodules():
             data = ''
 
         if 'bootstrap_cython_submodules' not in data:
-            data = data + """
+            data = ("""
 from %s.__bootstrap__ import bootstrap_cython_submodules
 bootstrap_cython_submodules()
-""" % (self.extension_name, )
+""" % (self.extension_name, )) + data
 
         with open(os.path.join(self.bootstrap_directory, '__init__.py'), 'w') as f_out:
             f_out.write(data)