diff --git a/Lib/imaplib.py b/Lib/imaplib.py
--- a/Lib/imaplib.py
+++ b/Lib/imaplib.py
@@ -255,6 +255,7 @@
     def shutdown(self):
         """Close I/O established in "open"."""
         self.file.close()
+        self.sock.shutdown(socket.SHUT_RDWR)
         self.sock.close()