Index: Lib/http/client.py
===================================================================
--- Lib/http/client.py	(revision 80784)
+++ Lib/http/client.py	(working copy)
@@ -601,7 +601,10 @@
     def getheader(self, name, default=None):
         if self.headers is None:
             raise ResponseNotReady()
-        return ', '.join(self.headers.get_all(name, default))
+        headers = self.headers.get_all(name, [])
+        if headers:
+          return ', '.join(headers)
+        return default
 
     def getheaders(self):
         """Return list of (header, value) tuples."""