diff -r 0dd6ac8ea523 Lib/test/test_urllib.py
--- a/Lib/test/test_urllib.py	Mon Apr 25 00:12:32 2016 +0300
+++ b/Lib/test/test_urllib.py	Wed Apr 27 10:15:48 2016 +0800
@@ -228,6 +228,7 @@
         # List of no_proxies with space.
         self.env.set('NO_PROXY', 'localhost, anotherdomain.com, newdomain.com')
         self.assertTrue(urllib.request.proxy_bypass_environment('anotherdomain.com'))
+        self.assertTrue(urllib.request.proxy_bypass_environment('ANOTHERDOMAIN.COM'))
 
 class urlopen_HttpTests(unittest.TestCase, FakeHTTPMixin, FakeFTPMixin):
     """Test urlopen() opening a fake http connection."""
diff -r 0dd6ac8ea523 Lib/urllib/request.py
--- a/Lib/urllib/request.py	Mon Apr 25 00:12:32 2016 +0300
+++ b/Lib/urllib/request.py	Wed Apr 27 10:15:48 2016 +0800
@@ -2472,9 +2472,9 @@
     if no_proxy == '*':
         return 1
     # strip port off host
-    hostonly, port = splitport(host)
+    hostonly, port = splitport(host.lower())
     # check if the host ends with any of the DNS suffixes
-    no_proxy_list = [proxy.strip() for proxy in no_proxy.split(',')]
+    no_proxy_list = [proxy.strip() for proxy in no_proxy.lower().split(',')]
     for name in no_proxy_list:
         if name and (hostonly.endswith(name) or host.endswith(name)):
             return 1