diff --git a/Lib/multiprocessing/managers.py b/Lib/multiprocessing/managers.py
index 7763965..f2cee0c 100644
--- a/Lib/multiprocessing/managers.py
+++ b/Lib/multiprocessing/managers.py
@@ -287,7 +287,7 @@
                 try:
                     send(msg)
                 except Exception, e:
-                    send(('#UNSERIALIZABLE', repr(msg)))
+                    send(('#UNSERIALIZABLE', format_exc()))
             except Exception, e:
                 util.info('exception in thread serving %r',
                         threading.current_thread().name)
diff --git a/Misc/NEWS b/Misc/NEWS
index dc4aa84..21cca5b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -125,6 +125,9 @@
 
 - Issue #25455: Fixed a crash in repr of cElementTree.Element with recursive tag.
 
+- Issue #21201: Improves readability of multiprocessing error message.  Thanks
+  to Wojciech Walczak for patch.
+
 IDLE
 ----