diff --git a/Lib/urllib.py b/Lib/urllib.py
index c7af8ec..a73c5d7 100644
--- a/Lib/urllib.py
+++ b/Lib/urllib.py
@@ -484,6 +484,8 @@
             urlfile = file
             if file[:1] == '/':
                 urlfile = 'file://' + file
+            elif file[:2] == './':
+                raise ValueError("local file url may start with / or file:. Unknown url of type: %s" % url)
             return addinfourl(open(localname, 'rb'),
                               headers, urlfile)
         host, port = splitport(host)