--- Lib/urllib.py
+++ Lib/urllib.py
@@ -28,6 +28,7 @@
 import time
 import sys
 from urlparse import urljoin as basejoin
+import warnings
 
 __all__ = ["urlopen", "URLopener", "FancyURLopener", "urlretrieve",
            "urlcleanup", "quote", "quote_plus", "unquote", "unquote_plus",
@@ -1281,7 +1282,10 @@
     for name, value in os.environ.items():
         name = name.lower()
         if value and name[-6:] == '_proxy':
-            proxies[name[:-6]] = value
+            if name == 'https_proxy':
+                warnings.warn ("urllib can't handle https proxies, your https_proxy setting will not work", RuntimeWarning, stacklevel=2)
+            else:
+                proxies[name[:-6]] = value
     return proxies
 
 if sys.platform == 'darwin':