diff -r bf5a899a5d7c Doc/library/sys.rst
--- a/Doc/library/sys.rst	Sun Apr 12 17:56:34 2015 -0400
+++ b/Doc/library/sys.rst	Sun Apr 12 21:06:38 2015 -0400
@@ -1001,6 +1001,9 @@
    function for further tracing in that scope), or ``None`` to turn off tracing
    in that scope.
 
+   If an exception is raised in the execution of the trace function, system
+   tracing will be disabled to prevent subsequent errors.
+
    The events have the following meaning:
 
    ``'call'``