diff --git a/nvchecker/source/pypi.py b/nvchecker/source/pypi.py
index 83b739b..a3d3014 100644
--- a/nvchecker/source/pypi.py
+++ b/nvchecker/source/pypi.py
@@ -1,6 +1,8 @@
 # MIT licensed
 # Copyright (c) 2013-2017 lilydjwg <lilydjwg@gmail.com>, et al.
 
+from pkg_resources import parse_version
+
 from . import conf_cacheable_with_name, session
 
 get_cacheable_conf = conf_cacheable_with_name('pypi')
@@ -15,7 +17,10 @@ async def get_version(name, conf, **kwargs):
     data = await res.json()
 
   if use_pre_release:
-    version = sorted(data['releases'].keys())[-1]
+    version = sorted(
+      data['releases'].keys(),
+      key = parse_version,
+    )[-1]
   else:
     version = data['info']['version']
   return version