diff --git a/Lib/xmlrpclib.py b/Lib/xmlrpclib.py
index e984baf551d1bec16b0d19f08c67ef141fd27293..5ef1cf9300ccc2ff80b1530d284f995a4a420a7e 100644
--- a/Lib/xmlrpclib.py
+++ b/Lib/xmlrpclib.py
@@ -1065,7 +1065,7 @@ class Transport:
 
         if auth:
             import base64
-            auth = base64.encodestring(auth)
+            auth = base64.encodestring(urllib.unquote(auth))
             auth = string.join(string.split(auth), "") # get rid of whitespace
             extra_headers = [
                 ("Authorization", "Basic " + auth)