diff --git a/Lib/urllib.py b/Lib/urllib.py
--- a/Lib/urllib.py
+++ b/Lib/urllib.py
@@ -133,7 +133,7 @@
         self.proxies = proxies
         self.key_file = x509.get('key_file')
         self.cert_file = x509.get('cert_file')
-        self.addheaders = [('User-Agent', self.version)]
+        self.addheaders = [('User-Agent', self.version), ('Accept', '*/*')]
         self.__tempfiles = []
         self.__unlink = os.unlink # See cleanup()
         self.tempcache = None