diff -r 7a3e67bfa417 -r 16b5df5792a8 mercurial/ui.py
--- a/mercurial/ui.py	Mon Dec 19 00:28:12 2016 +0530
+++ b/mercurial/ui.py	Mon Dec 19 02:15:24 2016 +0530
@@ -1086,7 +1086,7 @@
 
     def geteditor(self):
         '''return editor to use'''
-        if sys.platform == 'plan9':
+        if pycompat.sysplatform == 'plan9':
             # vi is the MIPS instruction simulator on Plan 9. We
             # instead default to E to plumb commit messages to
             # avoid confusion.