diff -r b2d238adf802 Lib/imaplib.py
--- a/Lib/imaplib.py	Wed Feb 18 08:56:47 2015 -0500
+++ b/Lib/imaplib.py	Wed Mar 25 18:17:48 2015 -0400
@@ -1313,7 +1313,7 @@
     def process(self, data):
         ret = self.mech(self.decode(data))
         if ret is None:
-            return '*'      # Abort conversation
+            return b'*'     # Abort conversation
         return self.encode(ret)
 
     def encode(self, inp):