--- a/mercurial/dispatch.py	Sun Apr 10 21:32:08 2016 +0000
+++ b/mercurial/dispatch.py	Sun Apr 10 20:55:37 2016 +0000
@@ -990,8 +990,7 @@
         output = ui.config('profiling', 'output')
 
         if output == 'blackbox':
-            import StringIO
-            fp = StringIO.StringIO()
+            fp = util.stringio()
         elif output:
             path = ui.expandpath(output)
             fp = open(path, 'wb')